GEOLOGICAL  SKETCHES 


OF    'I' UK 


PRECIOUS   METAL  DEPOSITS 


OF   THE 


WESTERN  UNITED   STATES, 


BY 


F.  EMMOXS  AND  G.  F.  BECKER, 


WITH  NOTES   ON 


LEAD  SMELTING  AT  LEADVILLE. 


EXTKArT  FKOM  Till:  'IK NTH  CKNSITS  OF  THE  CNITKD  STATES,  VOL.  XIII  "STATISTICS  AND 

OK  THE  1'KECIors  METAI 


\V  A  S  II I  N  G  T  O  X  : 

G  O  V  K  K  N  M  i:  X  T     P  R  I  N  T  I  N  U     O  F  F  ICE. 

1  8 


GEOLOGICAL  SKETCHES 


OF  THE 


PRECIOUS   METAL  DEPOSITS 


OF   THE 


WESTERN  UNITED   STATES, 


BY 


S.  F:  EMMOXS  AND  GfF.*  DECKER,    « 


? 


WITH    NOTES   ON 


LEAD  SMELTING  AT  LEADVILLE. 


EXTRACT  FROM  THE  TENTH  CENSUS  OF  THE  UNITED  STATES,  VOL.  XIII  "STATISTICS  AND 

TECHNOLOGY  OF  THE  PRECIOUS  META1 


\V  A  S  II  I  N  G  T  O  N  : 
GOVERNMENT    PRINTING    OFFICE. 

1885. 


oft  Ubnuy 


STATISTICS  AND  TECHNOLOGY  OF  THE  PRECIOUS  METALS. 


CHAPTER  I.— GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 

BY  GEORGE  F.  BKCKER. 

It  is  the  purpose  of  this  chapter  to  present  such  au  outline  of  the  geology  of  each  of  the  states  and  territories 
west  of  the  Rocky  mountains  as  will  serve  to  assist  those  unfamiliar  with  the  country  in  forming  an  idea  of  the 
character  and  distribution  of  its  mineral  resources,  and  to  convey  such  rudimentary  information  concerning  the 
relations  which  the  ore  deposits  bear  to  the  larger  features  of  the  geological  structure  as  is  necessary  to  an 
intelligent  perusal  of  the  statistical  chapters.  The  information  available  for  this  purpose  is  far  from  ample.  The 
government  geological  explorations  of  the  last  twenty  years  have  done  a  large  amount  of  extremely  valuable  work, 
Bme  of  which  has  made  a  permanent  mark  on  the  history  of  the  science;  but  the  territory  is  so  vast  that  many 
decades  must  elapse  before  even  the  preliminary  explorations  are  completed.  The  collections  and  the  data  gathered! 
by  the  census  experts  are  also  very  valuable.  Few  mines,  however,  can  be  properly  understood  without  a  somewhat 
extended  examination  of  the  surrounding  country,  for  which  the  experts  had  no  time,  and  the  information  is  therefore 
rather  fragmentary. 

The  order  adopted  in  sketching  the  states  and  territories  is  not  that  which  would  have  been  chosen  had  the 
information  been  more  complete.  Washington  territory  and  Oregon  are  placed  after  California,  because  little  is 
known  of  them  directly,  while  certain  inferences  maybe  legitimately  drawn  from  the  analogous  territory  embraced 
in  the  last-named  state,  and  Idaho  is  described  after  Nevada  and  Utah  for  similar  reasons. 

The  regularity  of  the  distribution  of  ores  in  the  Pacific  division  and  its  relations  to  the  singularly  uniform- 
topography  long  ago  drew  the  attention  of  writers  to  the  resources  of  this  region.  Mr.  W.  P.  Blake  (a)  first 
published  a  note  on  the  subject  in  1866,  and  his  statement  was  accepted  and  enlarged  upon  by  Mr.  King  (b)  in 
1870.  The  more  detailed  technical  and  scientific  investigations  of  later  years  have  greatly  increased  our  knowledge 
of  the  distribution  and  extent  of  the  ores,  and  it  will  now  scarcely  be  maintained  that  there  are  more  than  four  well 
defined  and  continuous  ore  belts  west  of  the  Rocky  mountains.  Beginning  at  the  east,  the  first  is  that  at  the 
western  foot  of  the  Wahsateh  and  the  southwestern  continuation  of  that  range.  With  the  exception  of  the  Leeds 
(Silver  Reef)  district,  all  the  important  ore  deposits  of  Utah  lie  in  the  foot-hills  of  this  range,  bearing  a  very  definite 
relation  to  the  main  line  of  crests.  The  gold  and  copper  belt  of  California  stands  for  a  long  distance  in  a  similar 
relation  to  the  Sierra  Nevada.  The  quicksilver  belt  in  the  California  coast  ranges  is  not  quite  so  regular  in  its 
occurrence,  yet  its  direction  is  very  nearly  parallel  to  the  coast,  and  it  is  very  persistent,  though  nowhere  broad,  for 
some  300  or  400  miles.  The  Arizona  belt  is  less  known  than  any  of  the  others,  but  no  one  can  glance  at  a  map  of 
the  territory  showing  the  mining  districts  without  perceiving  that  these  lie  in  a  northwestern  and  southeastern 
line  diagonally  across  the  country.  The  mining  districts  in  Nevada  are  extremely  numerous,  so  niHch  so  indeed 
that  some  grounds  could  be  given  for  assuming  a  belt  to  run  in  almost  any  desired  direction,  but  they  are  scarcely 
close  or  regular  enough  in  any  one  line  to  compel  the  observer  to  regard  them  as  connected. 

These  four  distinct  belts  appear  to  have  an  intimate  connection  with  the  four  great  orographical  changes  which 
the  region  west  of  the  Rocky  mountains  has  undergone  during  its  geological  history.  The  last  of  these  was  post- 
Miocene,  and  resulted  in  the  uplift  of  the  Pacific  Coast  ranges  and  the  great  interior  valley  of  California,  with  a  large 
part  of  Oregon  and  Washington  territory.  The  disturbing  force  seems  to  have  been  most  powerful  to  the  north  and 
south  of  San  Francisco,  or  approximately  in  the  region  marked  by  the  quicksilver  deposits.  A  post  Cretaceous, 
upheaval  raised  the  whole  western  central  portion  of  the  continent  now  occupied  by  the  complex  system  of  the 

a  Annotated  catalogue  of  the  principal  mineral  species  hitherto  recognized  in  California,  etc.  Report  to  state  board  of  agriculture, 
p.  26. 

»  Exploration  of  tkt  40(A  Parallel,  iii,  p.  5. 


6  PRECIOUS  METALS. 

Bocky  mountains.  The  Wahsatch  forms  the  western  edge  of  this  uplift,  ;mtl  the  dislocation  took  place  on  an  old 
fault  coincident  with  the  present  western  foot  of  that  range.  Here  also  lie  the  numerous  mines  of  Utah.  The 
Sierra  Nevada  and  the  ranges  of  the  Great  Basin  were  raised  by  a  post-Jurassic  uplift.  The  line  of  most  intense 
disturbance  coincided  with  the  Sierra,  and  the  greatest  dislocation  occurred  along  its  western  foot,  in  the  gold  belt, 
though  it  also  extended  to  the  south  of  that  wonderful  series  of  deposits.  The  earliest  disturbance  in  the  far  west 
was  that  which  raised  the  Palaeozoic  strata  of  eastern  Nevada,  western  Utah,  and  a  portion  of  Arizona  above  the 
surface  of  the  ancient  sea.  The  western  limit  of  this  Palaeozoic  area  has  been  traced  in  detail  across  the  belt 
surveyed  by  the  exploration  of  the  fortieth  parallel,  and  i^that  latitude  it  trends  nearly  north  and  south  in 
longitude  117°  30'.  To  the  south  the  limit  has  been  fixed  at  aw>nsiderable  number  of  points,  though  it  has  not  been 
followed  in  detail.  South  of  Austin  the  course  of  the  western  edge  of  the  Palaeozoic  is  somewhat  west  of  south,  and 
it  enters  California  a  little  north  of  Owen's  lake.  In  this  region  it  is  deflected  toward  the  southeast,  crosses  the 
Colorado  river  in  Virgin  canon,  passes  by  Prescott,  and  on  through  Arizona  to  the  neighborhood  of  Tombstone. 
The  main  Arizona  belt  of  deposits  has  the  same  trend  as  the  border  of  the  Palaeozoic,  and  nearly  coincides  with  it 
in  position.  In  short,  though  the  relation  still  requires  much  investigation,  the  Arizona  mineral  belt  appears  to 
stand  in  nearly  the  same  relation  to  the  western  edge  of  the  post-Carboniferous  upheaval  as  do  the  belts  of  Utah 
and  California  to  the  other  uplifts.  That  these  relations  exist  as  a  matter  of  fact  is  beyond  question,  though  it  is 
possible  that  they  may  be  accidental.  In  any  case,  however,  the  uplifts,  as  such,  are  not  to  be  regarded  as  the  cause 
of  the  formation  of  the  mineral  belts ;  these  must  rather  be  due  to  the  fissuring  of  the  rocks  and  the  dislocations 
attending  the  orographical  changes.  There  is  evidence  that  the  post-Carboniferous  uplift  in  the  state  of  Nevada 
and  in  southeastern  California  was  comparatively  gentle,  and  that  it  was  not  attended  by  any  considerable  crumpling 
of  the  strata.  This  would  account  for  the  fact  that  the  number  of  ore  deposits  'at  its  edge  in  these  states  is  not 
very  large.  Nevertheless,  the  lead  deposits  of  Battle  Mountain,  the  Austin  mines,  the  Candelaria  district  (which 
includes  the  famous  Northern  Belle  mine),  Panamint,  and  Cerro  Gordo  all  occur  at  or  close  to  the  western  edge  of 
the  Palaeozoic.  Taken  in  connection  with  the  geological  similarity  of  their  position  to  that  of  the  Arizona  mines, 
these  deposits  may  perhaps  fairly  be  regarded  as  the  rudiments  of  a  belt.  In  Arizona  the  area  in  which  the  contact 
occurs  has  been  too  little  investigated  to  allow  of  any  statement  as  to  the  violence  of  the  uplift,  but,  all  things 
considered,  it  would  be  remarkable  if  it  should  not  ultimately  prove  to  have  been  attended  by  much  disturbance. 

This  theory  of  a  relation  between  the  ore-belts  and  the  lines  of  uplift  is,  of  course,  not  to  be  understood  as 
equivalent  to  the  assertion  that  the  deposits  are  to  be  found  only  along  a  single  line  representing  the  actual  main 
fissure  of  the  uplift.  One  is  apt  to  think  of  the  dislocation  attending  an  orographical  change  as  confined  to  a  single 
vertical  or  highly  inclined  surface,  but  every  geologist  is  aware  that  this  is  not  an  exact  view.  Simple  fissures  in 
the  earth's  crust  are  very  rare,  and  parallel  sets  of  fissures,  with  cross  fractures  and  stringers  into  the  surrounding 
country,  are  the  rule  even  in  the  case  of  insignificant  cracks.  In  disturbances  such  as  those  of  the  great  uplifts 
a  considerable  belt  of  country  is  almost  necessarily  crushed  and  torn,  and  innumerable  rents  and  cracks  standing 
in  most  complex  relations  to  one  another  penetrate  the  rocks  in  many  directions.  The  breadth  of  such  a  zone 
must  usually  be  measured  in  miles. 

It  may  be  that  some  of  the  ore  deposits  of  the  Pacific  division  are  independent  of  volcanic  action,  but  the 
association  of  eruptive  rocks  with  ores  is  a  rule  with  comparatively  few  apparent  exceptions,  and  in  many  cases  the 
agency  of  solfataric  action  («)  is  manifest.  This  has  long  been  recognized  by  observers. 

That  there  are  relations  between  the  rocks  inclosing  ore  deposits  and  the  character  of  the  ores  has  been  known 
to  miners  for  centuries,  but  the  study  of  the  nature  of  this  dependence  is  comparatively  new.  It  is  far  too  complex 
a  subject  to  be  discussed  in  this  chapter,  but  it  may  at  least  be  stated  that  the  census  collections  and  data  appear 
to  confirm,  emphatically,  the  existence  of  such  relations.  Lead  ores  are  almost  invariably  accompanied  by  limestone, 
and  veins  in  granite  present  only  a  very  small  number  of  associations  of  minerals,  which  are  possibly  reducible  to 
a  single  one.  Deposits  in  metamorphic  rocks,  too,  though  more  varied  than  the  others,  appear  to  represent  but  a 
few  types.  It  was  not  practicable,  however,  for  the  experts  to  make  such  minute  examinations  of  the  mines  as 
would  have  been  necessary  to  furnish  material  for  a  conclusive  investigation  of  this  subject. 

With  some  hesitation  most  of  the  determinations  of  the  ore  and  gaugue  minerals,  the  country  rocks,  and  the  kind 
of  deposit,  are  introduced  county  by  county.  There  can  be  no  doubt  that  the  list  of  ore  minerals  is  often  imperfect. 
The  determination  of  the  wall  rocks  is  subject  to  some  uncertainty  without  a  thorough  examination  in  the  field  aa 
well  as  in  the  study,  and  the  nature  of  a  deposit  is  in  many  cases  not  to  be  decided  by  a  single  visit.  It  is 
probable,  however,  that  the  determinations  of  rocks  and  minerals  are,  nearly  always  correct  as  far  as  they  go,  and  in 
the,  cases  in  which  the  character  of  the  ore  deposits  was  not  clear  as  much  may  generally  be  inferred  from  the  statement 
regarding  them.  The  tables,  therefore,  contain  much  information  of  value,  and  many  suggestions  to  such  geologists 
and  miners  as  are  careful  to  remember  that  they  are  not  exhaustive  statements.  Except  in  a  few  cases,  in  which 
I  happened  to  have  visited  the  localities,  the  determination  of  the  character  of  the  deposits  rests  on  the  authority 
of  the  experts.  The  determinations  of  rocks  and  minerals  inclosed  in  parenthesis  are  also  due  to  the  experts, 


a  AH  originally  employed,  the  term  solfataric  action  denoted  only  the  effect  of  gaseous  emanations  from  volcanic  vents.  In  use, 
however,  it  has  gradually  coine  to  include  the  action  of  heated  waters  charged  with  these  giwes  or  holding  them  in  solution,  and  is  BO 
employed  in  this  chanter. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  7 

while  the  remainder  I  have  made  from  the  specimens  collected  by  my  assistants.  The  difficulties  met  with  in 
making  these  determinations  were  considerable,  for  rocks  near  ore  deposits  are  usually,  much  altered,  and  the  ore 
minerals  need  much  closer  attention  than  in  ordinary  specimens  of  merely  mineralogical  interest.  A  few  minute 
particles  of  such  minerals  in  a  hand  specimen  often  make  the  difference  between  waste  rock  and  rich  ore  and  the 
inspection  of  the  samples  needed  to  be  correspondingly  searching. 

Maps  of  the  states  and  territories  of  the  Pacific  division  accompany  the  sketches.  These  are  necessarily  on  a 
small  scale,  but  present  the  leading  features  sufficiently  well  to  assist  the  reader  in  following  the  descriptions.  On 
them  are  entered  signs  indicating  the  distribution  of  gold,  silver,  and  quicksilver.  These  are  not  designed  to 
represent  every  spot  where  precious  metals  have  been  detected,  but  to  indicate  at  a  glance  their  general  distribution. 

GEOLOGICAL  SKETCH  OF  CALIFORNIA. 

The  mineral  resources  of  California  are  extremely  varied,  but  are  also  of  very  unequal  importance.  Its  gold 
production  is  an  essential  factor  in  determining  the  relations  of  the  mediums  of  exchange  throughout  the  world,  its 
total  value  since  1849  exceeding  $1,200,000,000.  Its  quicksilver  production,  also,  though  of  far  less  value,  exceeds 
that  of  any  other  country.  The  total  known  product  of  California  from  1850  to  the  close  of  1880  was  a  trifle  less 
than  91,000,000  pounds,  of  an  average  value  of  71  cents,  and  has  yielded  above  $65,000,000.  It  is  important  as  an 
adjunct  to  the  precious-metal  industries  no  less  than  as  an  independent  source  of  profit.  The  silver  product  yields 
above  a  million  per  year ;  and  the  coal-fields,  though  not  of  the  best,  furnish  a  large  part  of  the  supply  necessary 
for  home  consumption.  Asphalt  and  petroleum  are  obtained  in  small  quantities,  and  some  sulphur  and  borax  are 
extracted,  while  lead  is  reduced  only  as  an  incident  of  the  silver  industries,  and  copper  and  iron,  though  their  ores 
are  plentiful,  are  worked  on  a  small  scale  only.  Tin,  chromic  iron,  black  oxide  of  manganese,  and  other  useful 
minerals  also  occur  in  the  state,  but  as  yet  contribute  little  to  its  commercial  prosperity. 

The  great  industrial  importance  of  the  gold  production  of  California  has  drawn  the  attention  of  many  geologists 
and  engineers  to  the  geology  of  the  state,  and  the  literature  on  the  subject  is  comparatively  extensive.  The  Pacific 
railroad  survey,  Mr.  J.  A.  Phillips'  work  on  gold  and  silver,  the  reports  of  the  mining  commissioners,  the 
proceedings  of  the  California  Academy  of  Sciences,  and  the  scientific  journals  of  America  and  Europe,  all  contain 
contributions  to  the  subject;  but  the  chief  source  of  authority  is  the  volumes  of  the  state  geological  survey  of 
California,  conducted  under  the  charge  of  Professor  J.  D.  Whitney,  who  had  the  assistance  of  Messrs.  Clarence 
King,  W.  H.  Brewer,  W.  M.  Gabb,  William  Ash  burner,  W.  H.  Pettee,  and  others.  Unfortunately,  the  legislature 
ceased  to  appropriate  funds  for  the  survey  in  1874  before  a  single  geological  map  had  been  issued.  Professor 
Whitney,  however,  has  continued  to  work  up  the  material  collected,  and  has  issued  a  number  of  volumes  during 
the  last  eight  years.  The  census  reports  and  collections  also  furnish  some  information  of  value  from  a  geological 
point  of  view,  but  the  following  sketch  owes  most  to  the  data  collected  by  Professor  Whitney  and  his  assistants 
or  recorded  in  the  volumes  published  under  his  supervision. 

The  interior  of  California  forms  a  long,  oval  valley.  Its  greater  diameter  is  parallel  to  the  coast,  and  extends 
from  th«  neighborhood  of  Fort  Tejon  to  Mount  Shasta,  a  distance  of  450  miles,  while  the  average  width  is  about 
40  miles.  This  valley  is  surrounded  by  mountains,  except  at  a  single  point,  where  San  Francisco,  San  Pablo,  and 
Suisun  bays  afford  an  outlet  for  the  drainage  gathered  by  the  Sacramento  river  from  the  north  and  the  San  Joaquin 
from  the  south. 

Though  the  mountain  ranges  inclosing  this  basin  unite  at  its  extremities,  the  Great  Valley  is  not  a  mere 
undisturbed  area  between  different  ranges  of  a  complex  chain ;  on  the  contrary,  the  Sierra  Nevada  to  the  east  and 
the  Coast  ranges  to  the  west  represent  upheavals  of  different  characters  and  widely  distant  eras.  The  Sierm 
Nevada  is  a  single  range  forming  the  western  rampart  of  the  elevated  plateau  of  the  Great  Basin,  and  was  raised 
in  post- Jurassic  times.  The  Coast  ranges  consist  largely  of  detritus  from  the  Sierra;  they  were  uplifted  for  the 
most  part  at  the  end  of  the  Miocene,  and  constitute  a  mountainous  belt  of  country  to  which  even  the  name  of 
chain  can  scarcely  be  applied.  No  term  answering  to  the  Coast  ranges  was  used  by  the  Spanish  settlers  of  the 
country,  but  they  gave  special  names  to  a  considerable  number  of  small  ranges  within  the  Coast  belt,  and  these  are 
still  in  use.  The  elevation  of  the  Coast  ranges  is  greatly  inferior  to  that  of  the  Sierra,  a  number  of  peaks  of  the 
latter  exceeding  14,000  feet,  while  none  of  the  culminating  points  of  the  Coast  ranges  appear  to  rise  more  than 
6,000  feet  above  sea  level. 

Both  the  Sierra  Nevada  and  the  Coast  ranges  are  greatly  metamorphosed  and  contain  extensive  deposits  of 
useful  minerals,  and  the  alteration  of  the  strata  and  the  deposition  of  ore  are  probably  in  each  case  related 
phenomena ;  but  the  metamorphosis  and  ore-deposition  of  the  Coast  ranges  occurred  long  after  the  cessation  of 
similar  activity  in  the  Sierra,  and  led  to  widely  different  results.  The  more  remarkable  deposits  of  the  Coast 
ranges  are  cinnabar,  chromic  iron,  coal,  asphalt,  and  mineral  oil,  Awhile  gold  and  copper  are  characteristic  of  the 
western  slope  of  the  Sierra,  lead  and  more  or  less  auriferous  silver  occurring  very  extensively  on  the  eastern  slope, 
of  which  only  a  portion  lies  within  the  limits  of  the  state. 

The  backbone  of  the  Sierra  is  granitic,  the  higher  summits  and  a  large  part  of  the  western  slope  of  the 
range  being  of  this  rock,  except  in  the  northern  portion  of  the  state,  where  it  has  been  covered  by  basaltic  and 


8  PRECIOUS  METALS. 

andesitic  lavas.  The  granite  penetrates  some  of  the  accompanying  strata  in  dikes,  and  Professor  Whitney  regaich 
it  as  beyond  question  of  eruptive  origin,  while  some  other  geologists  see  iu  it  only  highly  metainorphosed.seditnentary 
material  reduced  to  a  plastic  state  in  situ.  Except  at  the  northern  end  of  the  Great  Valley,  near  Mount  Shasta, 
and  near  Owen's  lake,  no  Palaeozoic  strata  have  been  identified.  lu  the  Gray  mountains,  Shasta  county,  a  limited 
area  of  Carboniferous  limestone  occurs,  amply  identified  by  fossils.  A  small  amount  of  limestone  with  the  same 
external  characteristics  occurs  farther  south,  and  Professor  Whitney  regards  it  as  not  improbably  of  the  same  age. 
From  a  mining  point  of  view,  however,  it  is  insignificant,  carrying  little  gold.  The  principal  strata  on  the  west  flank 
of  the  Sierra  are  Jurassic  and  Triassic,  occurring  chiefly  and  characteristically  as  slates  and  shales.  They  are  highly 
metamorphic,  contain  few  fossils,  and  have  been  profoundly  disturbed,  showing  that  the  range  was  uplifted  since  their 
deposition.  These  are  the  main  gold-bearing  rocks,  and  will  be  more  particularly  described  further  on.  Near  the 
foot  of  the  range  are  areas  of  Cretaceous  and  Tertiary  beds,  chiefly  marine,  nearly  horizontal,  and  resting  unconfoi-m- 
ably  on  the  upturned  auriferous  slates.  Above  the  Mesozoic  slates  lie  fresh-water  auriferous  gravels,  mainly  of 
Tertiary  age,  and  these  toward  the  north  are  in  part  covered  by  flows  of  Tertiary  and  post-Tertiary  lavas.  Inyo  and 
Mono  counties  lie  to  the  east  of  the  Sierra.  The  metamorphic  slates  and  limestones  of  this  region  are  for  the  most 
part  Triassic,  though  the  Jurassic  is  probably  also  represented,  and  are  covered  to  a  great  extent  by  volcanic  rocks. 
Mr.  Gilbert  has  shown  that  the  eastern  edge  of  Inyo  county  reaches  the  Paleozoic  area. 

The  Jura-Trias  strata  extend  to  the  east  of  the  Sierra  abont  as  far  as  longitude  117°  30'.  They  rest  directly 
upon  Archaean  schists  and  granite,  and  the  long  interval  of  time  which  they  represent  seems  to  have  been  extremely 
quiet,  for  no  non-conformity  has  been  detected  in  the  series.  At  the  close  of  the  Jurassic,  however,  the  whole 
area  from  the  western  foot  of  tbe  Sierra  to  the  middle  of  the  state  of  Nevada  was  raised  above  the  ocean  and 
compressed  from  west  to  east,  resulting  in  the  formation  of  a  number  of  parallel  ranges,  of  which  the  most  westerly 
were  the  Sierra  Nevada  and  the  Blue  Mountain  range  of  Oregon.  Ore  deposits  occur  on  the  eastern  as  well  as  on  the 
western  flank  of  the  Sierra,  but  their  character  and  mode  of  occurrence  differ  from  those  prevailing  in  the  gold  belt. 

The  Coast  ranges,  or  the  western  mountainous  belt  between  Mount  Shasta  and  fort  Tejou,  are  for  the  most  part 
composed  of  more  or  less  altered  rocks  of  Cretaceous  and  Tertiary  age.  The  geologists  and  the  paleontologists  of  the 
state  survey  divided  the  Cretaceous  into  lower  and  upper,  and,  while  recognizing  the  later  divisions  of  the  Tertiary, 
failed  to  find  anything  certainly  corresponding  to  Eocene.  Of  late,  however,  it  has  been  shown  that  the  fossils  of  what 
had  been  considered  as  the  Upper  Cretaceous  exhibit  strongly  marked  Tertiary  affinities,  and  it  seems  by  no  means 
impossible  that  the  beds  in  question,  which  are  sometimes  called  the  Tejon  group,  and  include  the  Monte  Diablo 
coal-fields,  really  represent  the  Eocene.  Considering  that  differences  of  climate  must  always  have  existed,  whether 
more  or  less  marked  than  those  of  the  present  time,  it  is  not  strange  that  doubtful  cases  like  those  of  the  Tejon 
group,  the  Laramie  beds,  and  the  Australian  coal-bearing  rocks  occur,  but  rather  that  it  is  so  often  possible  to 
determine  the  correspondence  of  strata  in  widely  separated  areas. 

Though  the  Coast  ranges  here  and  there  show  granitic  rocks,  granite  is  of  only  local  importance,  and  does  not 
appear  to  form  the  central  mass,  as  is  the  case  with  the  Sierra.  The  body  of  these  ranges  is  made  up  of  crumpled 
and  fractured  strata,  indicating,  according  to  Professor  Whitney,  sharp  and  sudden  elevations  and  depressions, 
extending  through  the  Pliocene  epoch.  To  the  southward  the  prevailing  rocks  are  Tertiary,  but  north  of  the  bay 
of  San  Francisco  these  almost  disappear,  the  Cretaceous  becoming  predominant.  Volcanic  rocks  are  not  widely 
spread,  most  of  the  known  occurrences  being  found  between  San  Francisco  and  Clear  lake. 

It  appears,  therefore,  that  the  elevation  of  the  coast  as  a  whole  was  comparatively  recent.  While  the  quartz 
veins  were  forming,  and  while  the  gravels  were  accumulating  ou  the  west  flank  of  the  Sierra,  the  region  of  the 
Coast  ranges  and  the  Great  Valley  were  wholly  or  partly  under  a  gulf  or  sea,  shallow  in  parts  and  surrounding 
more  or  less  extensive  islands.  The  existence  of  this  shallow  sea  must  have  had  an  important  influence  OH  the 
climate  of  the  Sierra,  for,  supposing  the  evaporation  to  have  been  the  same,  nearly  the  whole  amount  of  moisture 
now  distributed  through  the  Coast  ranges  and  the  interior  of  California  would  have  fallen  on  the  Sierra  in  addition 
to  its  present  rainfall.  But  evaporation  is  considerably  more  rapid  from  shallow  seas  than  from  deep  ones,  and 
the  rainfall  on  the  Sierra  must  consequently  have  been  enormous.  The  chief  uplift  of  the  Coast  ranges  took  place 
at  the  close  of  the  Miocene,  and  the  great  metamorphism  and  ore  deposition  are  probably  for  the  most  part  referable  to 
the  same  period,  though  it  is  likely  that  the  still  later  volcanic  eruptions  induced  a  portion  of  them.  The  Pliocene 
or  post-Pliocene  disturbances  were  comparatively  gentle,  but  Professor  Whitney  regards  the  break  at  the  Golden 
Gate,  the  prevalence  of  volcanic  rocks  from  that  point  north  to  Clear  lake,  and  the  disturbances  of  the  Pliocene 
south  of  San  Francisco  bay,  as  connected  phenomena. 

The  region  south  of  fort  Tejon  has  been  much  less  investigated  than  the  central  portion  cf  the  state.  It 
appears  to  possess  some  extremely  interesting  geological  features,  but  also  to  present  unusual  difficulties.  The 
San  Gabriel  range  north  of  Los  Angeles  has  a  granitic  axis,  and  it  is  possible  to  trace  this  granite  ridge 
uninterruptedly  through  Los  Angeles,  San  Bernardino,  and  San  Diego  counties  into  Lower  California,  and  along 
the  peninsula  to  within  a  few  miles  of  tbe  old  mission  of  Santa  Gertrudis.  (a)  The  sedimentary  rocks  accompanying 
this  granite  ridge  are  for  the  most  part  highly  metamorphosed,  and  are  frequently  penetrated  by  dikes  of  granite. 
They  are  nevertheless  considered  by  both  Professor  Whitney  and  Mr.  Gabb  as  of  Cretaceous  and  Tertiary  age,  and 
the  uplift  is  referred,  like  that  .of  the  Coast  ranges  proper,  to  the  close  of  the  Miocene. 


a  Geological  Survey  «f  California,  ii,  137. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  9 

« 

Besides  the  bitumen  springs  of  Ventura  and  Los  Angeles  counties,  there  are  gold  mines  in  this  southern 
California  range,  but  few  details  have  been  published  as  to  their  occurrence,  and  their  geological  relations  are  still 
to  be  studied. 

The  character  of  the  rocks  of  the  Coast  range  shows  that  the  Cretaceous  and  Tertiary  sea  near  the  present 
coast  was  shallow,  but  there  is  evidence  that  the  Great  Valley  represents  a  former  depression  of  immense  depth. 
This,  .however,  would  not  prevent  the  gulf  at  the  foot  of  the  Tertiary  Sierra  from  being  as  warm,  for  example,  as 
the  Gulf  of  Mexico,  for  the  temperature  of  the  water  of  a  land-locked  basin  depends  on  the  depth  of  the  inlet  to  it, 
and  if  this  is  small  the  water  of  the  basin  will  be  warm. 

In  Russia  and  Australia  the  Silurian  is  the  gold-bearing  formation,  and  Sir  Roderick  Murchisou  enunciated  the 
somewhat  rash  generalization  that  gold  was  to  be  looked  for  only  in  the  Palaeozoic.  In  California  it  is  amply  proved 
by  rare,  but  characteristic  fossils  that  the  gold-bearing  sedimentary  rocks  are  Mesozoic.  Generalizations  similar  to 
Murchison's  have  been  attempted  with  reference  to  ores  of  other  metals,  but  the  simple  fact  seems  to  be  that 
eruptive  activity  or  inetamorphisin  is  usually  a  concomitant  of  the  concentration  of  ores  in  veins  and  other  allied 
deposits,  and  that  the  older  the  rocks  the  greater  the  general  probability  that  they  will  have  been  subjected  to 
action  of  this  description.  In  the  search  for  coal  the  fact  that  the  important  deposits  of  the  best  character  are 
confined  to  one  formation  has  been  of  great  economical  value.  The  geological  indications  accompanying  the 
occurrence  of  veins  are  to  be  sought,  not  in  the  age  of  the  rocks,  but  in  evidences  of  disturbance  and  of  certain  kinds 
of  decomposition  of  the  surrounding  country.  The  decomposition  or  alteration  of  rocks  in  the  neighborhood  of  ore 
deposits  has  been  but  little  studied  by  geologists  until  lately,  for  very  sufficient  reasons;  but  of  the  fact  of  a 
connectiou  between  it  and  the  deposition  of  ore  California  affords  excellent  examples.  The  "bed-rock"  or 
auriferous  slates  of  the  gold  belt  is  characteristically  altered,  and  the  metamorphic  stratum  in  which  cinnabar  occurs 
art-  at  once  recognized  by  those  familiar  with  them  as  "quicksilver  rock". 

The  belt  of  metamorphic  rocks  which  incloses  the  greater  part  of  the  gold-quartz  veins  of  California  is  insignificant 
in  width  and  of  little  industrial  importance  south  of  the  southern  boundary  of  Mariposa  county.  To  the  north  of 
that  line,  however,  it  suddenly  widens.  Passing  northward,  the  breadth  of  the  belt  is  stated  at  about  25  miles 
in  Tuolumne  county,  24  miles  in  Calaveras,  12  in  Amador,  and  30  in  El  Dorado.  In  Placer  it  is  not  well  exposed, 
being  covered  by  gravel  and  volcanic  rocks.  North  of  Placer  county  the  metamorphics  occupy  most  of  the  western 
slope  of  the  range  for  a  considerable  distance,  with  occasional  irregularly  distributed  patches  of  granite,  but  in 
Uutte  county  the  edge  of  the  great  lava  fields,  which  occupy  much  of  the  surface  of  northeastern  California,  are 
encountered,  and  cut  off  the  central  mining  region.  The  same  gold-bearing  series  seems  to  reappear  in  the  north- 
western counties,  but  its  character  and  relations  are  less  well  understood,  and  its  industrial  importance  is  smaller 
than  in  central  California. 

As  illustrative  of  the  structure  of  the  gold  belt,  Professor  Whitney  describes  in  some  detail  the  important 
portion  lying  between  the  Merced  and  the  Stanislaus  rivers.  Starting  from  the  west,  or  at  the  bottom  of  tb«  Sierra, 
the  first  rock  encountered  is  horizontally  stratified  and  undisturbed  Tertiary  sandstone.  To  this  succeeds  the  belt 
of  Mesozoic  metamorphics  in  nearly  vertical  strata.  The  lower  edge  is  composed  of  talcose  and  chloritic  slates, 
weathering  irregularly,  and  locally  known  as  "grave-stone"  slates.  Next  comes  a  wide  belt  of  a  dark-grayish 
green,  somewhat  porphyritic,  material,  which  shows  a  sheeted  structure,  though  not  the  fine  lamination  of  clay 
slates.  This  was  known  to  the  state  survey  as  i( porphyritic  green  slate",  but  Professor  Whitney  and  Mr. 
Wadsworth  are  inclined  to  regard  it  as  a  metamorphosed  diabasitic  tufa.  This  belt  incloses  another  of  argillaceous 
slate,  carrying  Jurassic  fossils,  with  which  is  associated  the  "mother  lode",  or  the  "great  quartz  vein". 
Accompanying  the  argillaceous  slate  and  the  mother  lodeisa  band  of  serpentine,  (a)  In  the  southern  portion  of  this 
section  the  seqjeutine  is  confined  to  the  northeast  side  of  the  argillaceous  slate,  but  near  the  Stanislaus  river  it 
widens  out,  occurring  in  irregular  patches  and  on  both  sides  of  the  slates. 

The  strike  of  the  metamorphosed  rocks  is,  as  a  whole,  parallel  to  the  trend  of  the  Sierra,  but  there  are  many 
sharp  deflections.  The  dip  of  the  slates  in  the  southern  and  central  portion  of  the  gold  belt  is  nearly  vertical,  and 
usually  to  the  northeast;  but  in  the  northern  portion,  where  the  belt  widens  out,  the  dip  becomes  irregular,  and  over 
wide  areas  is  to  the  west,  becoming  natter  as  the  distance  from  the  crest  of  the  range  increases. 

Though  not  confined  to  the  argillaceous  slates,  or  even  to  the  metamorphic  strata,  the  gold-quartz  veins  of 
California  are  more  frequent  and  richer  in  the  argillaceous  slates  than  elsewhere,  many  fine  veins  beside  the 
"mother  lode"  occurring  in  it.  The  veins  are  usually  parallel  to  the  stratification,  as  the  following  quotation 
shows  :(b) 

A  very  heavy  quartz  vein  passes  a  little  south  ef  Big  Oak  Flat,  Tuoluume  county,  cutting  the  strata  of  slate  in  which  it  is 
contained  at  a  small  angle,  the  lines  of  bedding  of  the  wall-rock  appearing  to  run  nearly  northwest  and  southeast,  while  the  vein  of 
quartz  has  a  strike  of  N.  30°  W.;  it  dips  to  the  tast  at  tin  angle  of  30°,  the  slates  themselves  standing  nearly  vertical.  This  is,  perhaps 
the  most  marked  instance  hitherto  observed  in  the  state  of  a  heavy  quartz  vein  differing  essentially  both  in  dip  and  strike  from  the 
inclosing  rucks. 

a  The  origin  of  serpentine  is  a  disputed  point.  If  it  is  a  fact,  as  eminent  mineralogists  have  maintained,  that  it  occurs  as  an  alteration 
of  hornblende  and  pyroxene  as  well  as  of  olivine,  there,  appears  t«  be  no  difficulty  in  accounting  for  its  presence  in  metamorphic  rocks. 
Chlorite  and  serpentine,  however,  are  •ccusioually  confounded. 

b  Geological  Surrey  of  California :  Geology,  vol  I,  p.  237. 


10  PRECIOUS  METALS. 

The  most  remarkable  primary  metalliferous  deposit  of  California  is  the  mother  lode  already  referred  to.  Many 
of  tho  great  mines  of  the  state  are  upon  it,  and  others  are  in  its  immediate  vicinity  on  veins  which  most  likely  have 
an  intimate  structural  connection  with  it.  It  extends  from  a  point  a  few  miles  southeast  of  the  Merced  river,  iu 
Mariposa  county,  to  near  the  center  of  Amador,  a  distance  of  about  80  miles.  Though  the  croppings  are  in  places 
hidden  by  overlying  rock  or  detritus,  they  are  visible  for  a  great  portion  of  the  distance  at  such  frequent  intervals 
that  the  identity  of  the  lode  is  not  doubtful.  It  is  more  than  probable  that  it  extends  to  the  north  of  the  point, 
indicated,  but  it  cannot  be  traced  with  absolute  certainty. 

This  powerful  lode  (a)  is  made  up  of  irregularly  parallel  plates  of  white  compact  quartz  aud  crystalline  dolomite  or  uiagnesite  (6) 
more  or  less  mixed  with  green  talc;  and  these  plates,  which  somewhat  resemble  the  "combs"  of  ordinary  lodes,  are  either  in  contact  or 
separated  from  each  other  by  intercalated  layers  of  talcose  slate.  The  quartz  is  chiefly  developed  in  the  central  portion  of  tho  vein;  and, 
from  its  color  and  resistance  to  decomposition,  it  gives  rise  to  a  very  conspicuous  outcrop,  forming  the  crest  of  the  hills,  so  that  it  can  be 
readily  seen  from  a  distance  of  several  miles.  The  dolotnitic  or  magnesitic  portion  decomposes  somewhat  readily,  and  it  becomes  a  kind 
of  "gossan  "or  cellular,  ferruginous  mass,  of  a  dark-brown  color,  often  traversed  in  every  direction  by  seams  of  white  quartz.  The  quartz 
is  the  auriferous  portion  of  the  lode,  although  it  is  far  from  being  uniformly  impregnated  with  gold.  Most  of  the  mines  which  have  been 
worked  between  the  Merced  and  the  Stanislaus  are  on  the  northeast  side  of  the  great  quartz  vein,  either  in  contact  with  it  or  in  some 
parallel  band  of  quartz  subordinate  to  or  at  a  little  distance  from  it.  The  talcose-slate  bands  in  the  vein  are  often  themselves  more  or 
less  auriferous. 

Professor  Whitney  does  not  regard  it  as  by  any  means  proved  to  be  a  fissure  vein,  or  even  an  exclusively 
segregated  one;  on  the  contrary,  it  seems  to  him  most  likely  the  result  of  metamorphic  action  on  a  belt  of  rock  of 
peculiar  composition,  and  perhaps  originally  largely  dolomitic  in  character. 

Besides  the  quartz  veins  in  the  metamorphics  of  California,  there  are  also  many  in  the  granites  of  the  same 
region.  Though  of  less  importance  than  those  in  the  sedimentary  rocks,  many  of  them  have  been  worked  with 
profit,  but  no  careful  comparison  has  been  instituted  between  the  two  classes  of  veins.  In  some  instances  at  least, 
and  when  near  the  slates,  the  veins  in  the  granite  are  parallel  to  the  stratification  of  the  metamorphic  rocks,  and 
are  also  essentially  gold  veins.  It  is  probable,  however,  that  on  closer  investigation  they  will  be  found  to  present 
characteristic  differences. 

Gold  never  occurs  in  nature  unassociated  with  silver,  and  silver,  it  is  said,  is  never  wholly  free  from  gold  ;  but 
there  seems,  nevertheless,  to  be  a  natural  distinction  between  gold  veins  and  silver  veins.  In  Nevada,  Arizona, 
and  throughout  Mexico  gold  usually  occurs  only  in  minute  particles  entangled  in  sulpho-salts  of  silver  and  other 
metals,  except  near  the  surface,  where  atmospheric  action  has  decomposed  the  original  matrix.  Though  the  value 
of  the  gold  in  such  cases  sometimes  equals  or  exceeds  that  of  the  accompanying  silver,  the  latter  usually  greatly 
surpasses  it  iu  weight.  In  the  gold  belt  of  California,  on  the  other  hand,  the  gold  occurs  in  great  part  as  flakes  or 
even  as  masses,  often  not  immediately  iu  contact  with  sulphides,  and  carrying  in  alloy  only  0.100  or  0.200  of 
metallic  silver.  As  a  rule,  the  gold  does  not  assume  a  crystalline  form  in  the  California  mines,  but  more  or  less 
perfect  octohedral  forms  have  been  found  at  Spanish  Dry  Diggings  and  at  Byrd's  valley.  Cubical  crystals  have 
not  until  lately  been  observed,  and  Professor  Whitney  notes  that  he  has  neither  seen  nor  heard  of  any  in  the  state,  (c) 

Sulphides  always  accompany  the  gold  iu  the  veins,  though  these  minerals  are  not  always  found  in  contact  with 
the  larger  particles  of  the  metal.  So  general  is  the  association,  however,  that  when,  as  is  often  the  case  even  with 
rich  quartz,  the  gold  is  not  visible  to  the  naked  eye,  miners  judge  of  the  value  of  the  ore  by  the  quantity  of 
sulphnrets.  Quartz  with  plenty  of  sulphurets  and  no  visible  gold  often  occurs  in  large  bodies,  and  is  apt  to  pay 
better  in  the  long  run  than  ore  with  very  coarse  gold,  or  "  specimen  quartz",  as  it  is  called  by  the  miners.  The 
minerals  embraced  under  the  term  "sulphurets"  are  considerable  in  number,  but  the  most  common  are  pyrite, 
mispickel,  ziucblende,  and  galena.  Though  seldom  containing  the  greater  part  of  the  gold,  it  is  rarely  that  the 
sulphurets  do  not  include  a  portion  of  the  metal  in  such  a  way  that  it  cannot  be  extracted  by  amalgamation. 
Concentration  of  the  sulphurets,  followed  by  chloridatiou,  is  then  the  readiest  means  of  extraction.  There  is  an 
occurrence  of  cinnabar  in  gold  quartz  veins  inclosed  in  slate  in  Calaveras  and  one  in  Mariposa. 

The  distribution  of  gold  in  the  veins  is  usually  very  irregular,  and  while  on  some  veins  it  will  pay  to  extract 
the  ore  from  wall  to  wall,  in  most  cases  certain  belts  or  chimneys  of  rock  only  are  remunerative. 

Had  the  veins  been  deposited  in  the  slates  before  they  were  raised  into  their  present  position  in  post- Jurassic 
times,  they  must  have  been  much  faulted  and  broken.  This  is  not  the  case,  nor  is  it  probable  that  veins  could 
have  formed  in  undisturbed  strata.  On  the  other  hand,  there  can  be  no  doubt  that  the  auriferous  gravels  have 
been  formed  at  the  expense  of  eroded  croppings  of  the  quartz  veins ;  and  the  veins,  or  most  of  them,  must  therefore 
have  been  deposited  before  the  gravels.  These,  according  to  Professor  Whitney,  were  accumulated  during  the  whole 
of  the  Tertiary  period,  while  Cretaceous  gravels  appear  to  be  entirely  absent.  The  range  was  above  water  during 


a  Professor  Whitney:  Auriferous  Gravels,  p.  46. 

It  In  the  only  specimen  which  has  thus  far  been  chemically  examined  the  supposed  dolomitic  portion  proves  to  be  an  intimate  mixture 
of  quartz  and  magnesite.  • 

o  In  December,  1882,  however,  Mr.  James  Terry  purchased  a  specimen  of  gold  from  Louis  Abraham,  Kearney  street,  San  Francisco, 
which  is  said  to  have  come  from  Eldorado  county,  between  Plumas  and  Placerville,  which  shows  a  number  of  fine  cubical  crystals  witk 
full  faces  and  sharp  edges.  The  same  specimen  also  shows  well-developed  dodecahedrons,  trapezohedrons  combined  with  the  cube  and 
octohedron,  a  cube  the  corners  of  which  are  truncated  by  a  trapezohedron,  and  possibly  other  combinations. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  11 

the  Cretaceous,  jiud  such  fresh- water  deposits  as  accumulated  ou  its  west  slope  seem  to  have  beeu  swept  away 
during  the  succeeding  period.  The  natural  inference  would  seem  to  be  that  the  formation  of  the  veins  occurred 
between  the  end  of  the  Jurassic  aud  the  beginning  of  the  Tertiary,  and  that  it  was  intimately  connected  with  the 
upheaval  of  the  Sierra  and  the  metamorphisin  of  the  strata  of  preceding  epochs. 

Substantially  coincident  with  the  area  of  gold  veins  is  that  of  the  auriferous  gravels  of  California.  In  the 
gold  bearing  regions  of  all  countries  secondary  deposits  of  the  metal,  associated  with  gravel  or  sand,  have  played  ;i 
large  part,  because  the  gold  may  be  separated  from  such  loose  material  at  a  low  cost.  In  California,  however,  the 
gravels  have  proved  particularly  important  because  of  the  invention  and  development  there  of  the  peculiar  system 
of  hydraulic  mining,  which  consists  in  washing  the  gravels  into  sluices  provided  with  quicksilver  by  the  aid 
of  powerful  jets  of  water.  The  great  importance  of  this  system  is  due  to  the  fact  that  it  is  among  the  least 
costly  methods  of  handling  material,  if  it  is  not  the  very  cheapest  known.  It  costs  under  favorable  circumstances 
but  five  cents  per  cubic  yard,  or,  say,  three  cents  per  ton,  and  sometimes  even  less.  It  thus  renders  deposits 
of  gravel  valuable  which  under  most  conditions  would  be  absolutely  worthless.  Several  conditions,  however,  are 
necessary  to  the  successful  prosecution  of  hydraulic  mining,  among  which  the  most  important  are  a  deep  gravel 
bank,  abundance  of  water  with  a  great  head,  and  some  available  valley  at  a  lower  level  than  the  bank,  into  which 
the  gravel  from  which  the  gold  has  been  extracted  may  be  washed.  The  topographical  and  climatic  conditions  in 
the  Sierra  are  peculiarly  favorable  for  this  process,  while  in  Australia,  where  gravel  is  abundant,  circumstances 
rarely  permit  the  application  of  this  method  of  extraction. 

The  gravel  consists  of  bowlders  and  pebbles  of  various  rocks,  with  silt,  clay,  and  volcanic  ash.  The  gold  occurs 
as  nuggets  and  fine  particles,  free  or  nearly  free  from  rock,  but  also  as  fragments  of  gold  quartz,  and  is  accompanied 
by  a  variety  of  other  heavy  substances,  as  magnetite,  garnet,  and  zircon;  rarely  and  locally  also  by  cinnabar, 
platinum  and  iridosmine,  diamonds,  native  copper,  and  other  substauces  of  high  specific  gravity.  One  of  the  striking 
features  of  most  deep  gravel  banks  is  the  so-called  "blue  lead".  This  name  is  applied  to  the  lower  portions 
of  banks,  which  are  generally  somewhat  closely  compacted  and  possess  the  color  of  the  blue  clays  occurring  all  over 
the  world.  Although  the  "  blue  lead"  has  led  to  wholly  untenable  theories  as  to  the  character  of  the  gravel  deposits, 
its  nature  is  very  readily  accounted  for.  Loose  materials  n*>ar  the  earth's  surface  are  every  where  impregnated  with 
a  small  amount  of  organic  matter  carried  down  from  the  surface  by  water  and  filtered  from  it  by  the  porous  strata. 
This  organic  matter,  in  the  absence  of  free  oxygen,  exercises  a  slow  but  inevitable  reducing  action  ou  ferric  oxide 
and  on  some  ferric  compounds,  and  gives  the  soil  the  bluish  color  characteristic  of  the  presence  of  iron  in  the 
ferrous  state.  Close  to  the  surface,  however,  oxygen,  either  gaseous  or  in  aqueous  solution,  more  than  counterbalances 
the  reducing  action  of  the  organic  matter,  and  above  a  certain  line  the  gravel  is  consequently  reddened  by  ferric 
oxide.  In  shallow  deposits  the  gravel  is  usually  reddened  to  the  bottom,  but  of  course  this  does  not  aecessarily 
imply  that  such  gravels  have  a  different  origin  from  those  of  a  bluish  tint. 

To  a  very  large  extent  the  deep  gravels  are  covered  by  a  capping  of  volcanic  material,  sometimes  as  solid  black 
basalt,  and  sometimes  as  loose  volcanic  "  ash";  and  while  some  banks  are  not  thus  covered,  these  are  rarely  at  any 
great  distance  from  volcanic  capping.  The  volcanic  material  has  protected  the  gravels  in  many  cases  from  erosion, 
but  there  is  also  a  connection  in  their  deposition.  The  gravels  occur  in  ancient  river  beds,  which  formed  the  natural 
channels  for  the  flow  of  lava  as  well  as  of  water.  Volcanic  eruptions  occurred  during  the  period  of  the  gravel 
formation,  as  well  as  at  its  close,  and  sheets  of  ash  or  even  of  solid  lava  are  found  in  the  banks  as  well  as  upon 
them.  When  the  lava  cap  is  thick  and  solid  the  gravels  can  only  be  mined  by  drifting,  and  are  not  workable  by 
the,  hydraulic  process. 

Besides  the  deep  gravels,  which  date  from  a  period  prior  to  the  volcanic  eruptions,  there  are  many  accumulations 
of  recent  origin.  The  bars  of  the  present  river  system  have  yielded  great  quantities  of  gold,  and  there  are  many 
shallow  placer  deposits  which  are  no  doubt  due  to  the  modern  erosion  of  quartz  croppings,  while  others  are  a 
consequence  of  the  erosion  of  older  gravels.  The  modern  gravels,  however,  are  trifling  in  quantity  as  compared 
with  the  older  deposits.  Some  of  the  shallow  placers  are  no  doubt  mere  remnants  of  deeper  Tertiary  gravels  which 
have  not  beeu  wholly  carried  away  by  the  erosion  of  the  present  epoch. 

The  bed-rock  of  the  gravel  deposits  varies  in  character,  being  either  limestone,  granite,  or  metamorphic  slate; 
but  the  last  is  the  rule,  and  few  important  deposits  occur  far  from  the  slate  bed-rock,  which,  as  has  been  explained, 
is  the  main,  though  not  the  exclusive,  habitat  of  the  gold  veins.  In  nearly  all  cases  the  gravel  rests  in  local 
depressions,  early  recognized  by  the  California  miners  as  the  beds  of  former  streams.  Many  of  the  gravels,  it  is 
true,  are  high  above  the  present  drainage  system,  and  even  form  the  tops  of  hills;  but  this  is  due  to  the  erosion  of 
the  present  stream-beds,  which  have  been  cut  down  to  a  great  depth  since  the  gravel  period.  The  bed-rock  is 
usually  rough,  consisting  of  nearly  vertical  slates,  and  the  natural  crevices,  or  "  riffles",  large  and  small,  thus  formed 
often  contain  extremely  rich  gravel.  As  might  naturally  be  supposed,  the  greater  part  of  the  gold  is  generally 
found  near  the  bed-rock,  for  as  gold  is  about  seven  times  as  heavy  as  ordinary  rock  every  disturbance  of  a  gravel 
bar  in  a  stream  tends  to  shift  the  gold  to  a  lower  level.  Sometimes,  however,  rich  gravel  is  again  deposited  over  a 
comparatively  firm  stratum  in  the  gravel,  and  occasionally  gold  is  quite  uniformly  disseminated  through  a  whole 
bank. 


12 


PRECIOUS  METALS. 


An  idea  has  been  current  in  the  mining  region  that  by  some  process  masses  of  gold  in  the  gravel  have  increased 
in  size.  For  this  there  is  absolutely  no  valid  evidence.  The  rounded  masses  of  gold  found  could  not  have  been 
deposited  from  solution  in  that  form  or  with  such  a  surface.  They  have  been  beaten  and  worn  into  shape,  much  as 
the  accompanying  pebbles  have  been  formed,  the  only  difference  being  due  to  the  fact  that  gold  is  malleable. 
Professor  Whitney  believes  it  probable  that  the  higher  croppings  of  the  gold  veins  were  richer  and  contained  larger 
masses  of  gold  than  the  lower  portions  of  the  veins  still  in  place,  and  if  there  was  any  difference  at  all  it  was 
probably  of  that  character.  As  Professor  Newberry  (a)  points  out,  however,  the  gravels  represent  vastly  more 
vein-quartz  than  has  been  extracted  by  deep  mining,  and  the  proportion  of  large  masses  of  gold  met  with  in  the 
veins  probably  bears  as  great  a  ratio  to  the  total  weight  of  quartz  extracted,  as  do  the  nuggets  in  the  gravels  to  the 
quartz  from  which  their  metallic  contents  were  derived. 

The  investigations  of  the  state  survey  have  shown  that  the  deep  gravels  were  deposited  by  rivers  which 
headed  in  the  high  Sierra  and  ran  in  a  westerly  direction,  emptying  into  the  sea,  which,  in  Tertiary  time,  occupied 
the  great  valley  of  California.  Although  all  the  details  of  the  former  river  system  cannot  now  be  traced  out,  the 
courses  and  relations  of  the  channels  developed  by  hydraulic  mining  seem  to  establish  this  point  beyond  a  question. 
There  were  two  great  rivers  in  the  Pliocene  epoch,  one  corresponding  to  the  American  and  the  other  to  the  Yuba; 
but  the  Bear  river  of  that  time  probably  emptied  into  the  American  at  a  considerable  height  above  the  valley. 

The  gravels  cannot  possibly  have  accumulated  under  the  present  conditions  of  precipitation.  A  far  greater 
erosive  power  than  that  exhibited  by  the  California  streams  of  to-day  must  have  been  exerted  at  the  time  in 
question,  as  no  one  can  doubt  who  has  ever  visited  the  gold  belt.  For  a  long  time  past  the  present  rivers  have 
merely  been  deepening  their  narrow  courses,  and  when  freshets  occur  they  merely  serve  to  sweep  the  canons  clear 
of  debris,  but  cannot  alter  the  course  of  the  stream.  The  width  of  the  old  channels,  as  well  as  the  character  of 
the  deposits,  shows  that  the  old  rivers  were  tumultuous  streams  of  great  volume,  which  frequently  burst  their  bounds 
and  formed  new  beds. 

The  evidence  of  enormous  erosive  power  during  the  deposition  of  the  gravel  has  been  so  apparent  to  all 
observers  that  some  of  them  have  called  in  the  action  of  great  glaciers  to  account  for  the  occurrence  of  the  deposits. 
According  to  Professor  Whitney  this  is  incorrect ;  indeed,  lie  holds  that  the  former  glaciers  of  the  Sierra  did  not 
come,  into  existence  until  after  the  greater  part  of  the  gravels  occupied  their  present  position.  The  bed-rock  which 
the  gravels  cover,  and  which  they  have  protected  uot  only  from  erosion  but  even  from  atmospheric  action,  shows 
no  traces  of  glacial  polishing  and  scratching.  This  is  in  marked  contrast  to  the  higher  regions  of  the  range,  where 
the  glacial  markings  are  almost  as  fresh  as  in  the  Alps.  Nor  are  occurrences  frequent  which  can  possibly  be 
confounded  with  moraines,  while  the  fossils  found  indicate,  according  to  Mr.  Lesquerenx,  a  climate  a  few  degrees 
warmer  than  that  of  the  present  time. 

Professor  Whitney  believes  the  great  precipitation  necessary  to  account  for  the  large  rivers  of  the  Tertiary  in 
California  to  have  been  mainly  due  to  the  prevalence  of  higher  temperatures  at  that  period  and  to  the  accompany i:,g 
increased  evaporation  from  the  surface  of  tlie  ocean.  It  is  at  least  conceivable  that  the  climate  should  have  been 
something  like  that  of  the  Khassia  hills,  upon  parts  of  which  the  hot  winds  from  the  bay  of  Bengal  deposit  some 
500  inches  of  rain  yearly.  The  presence  of  a  sea  at  the  foot  of  the  range  must  have  largely  increased  the  rainfall, 
as  has  been  pointed  out.  It  is  to  be  inferred  from  Professor  Whitney's  remarks  that  he  supposes  the  climate  of 
the  Sierra  to  have  been  too  warm  for  glaciers  during  the  Tertiary.  He  regards  the  present  climate,  on  the  other 
hand,  as  too  dry  to  permit  of  their  formation,  though  there  can  be  no  doubt  of  their  existence  in  the  higher  part  of 
the  range  above  the  gold  belt  up  to  within  a  comparatively  short  time.  A  few  small  glaciers  on  the  northern 
slopes  of  mount  Shasta  are  now  the  only  remnant  of  the  former  ice  system  of  the  state.  The  Sierra  glaciers  were 
of  the  mountain  type,  however,  comparable  at  their  greatest  'extension  with  those  of  modern  Switzerland,  and 
nothing  like  a  general  glaciation  or  a  diluvial  period  ever  existed  in  California. 

The  following  sections  of  auriferous  gravel  deposits  are  selected  from  a  large  number  furnished  by  the  reports 
of  the  special  experts  to  illustrate  the  mode  of  occurrence  of  the  gravels  in  various  portions  of  the  state  : 

BONANZA  MINE. 
MOKEL0MNE  HILL  DISTRICT,  CALAVEEAS  COUNTY,  CALIFORNIA. 


I 

II 

III 

IV 


Lava  cap  in  places. 

Alternating  fine  and  coarse  sand  with  pebbles  (chiefly  quartz) . 
Cement, 
sesquioxide  of  iron. 

Bed-rock,  slate. 


A  quartzose  (also  granitic  and  slaty)  conglomerate,  cemented  with 


>  Maximum,  123  feet;  avetage,  75  feet. 


Richest  portion  nsnnlly  lower  15 
feet  above  bed-rock.  ID  place* 
gold  nearly  evenly  disseminated 
throughout  deposit. 


The  ancient  channel  on  which  this  mine  is  located  is  traceable,  with  intermittent  breaks,  for  10  miles.     The  channel  is  500  feet  wide,  the  outer  edges  barren, 
and  the  pay  channel  is  300  feet  wide. 


o  School  of  Mine*  Quarterly,  November,  1881. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


13 


LAGRANGE  HYDRAULIC  MINE. 
LAGRANGE  DISTRICT.  STANISLAUS  COUNT  Y,v  CALIFORNIA. 


II 
m 

IV 

v 


Red  sand 

Coarse  red  gravel,  containing  pebbles  of  granite,  etc.. 


Red  cement  ( ' ' hard-pan "). 

White  siliceous  clay 

Red  cement  (same  as  HI) 

VI      Sand  with  pebbles 

VII      Loose  yellow  sand 

VTII      Dark-colored  gravel,  containing  dtbris  of  granite,  argillaceous  slate,  "  ser- 
Dentine,"  etc.,  with  some  quartz. 

IX      Bed-rock  at  Lagrange  "dioriteand,  slate";  at  Patricksvillc  "basaltic  tufa" 
(no  specimen). 


'  Maximum,  300  feet ;  average,  40  feet. 


Lowest  6  feet  8  inches  riohest. 


Quartz  forms  but  a  small  proportion  of  the  gravel,  which  is  chiefly  granite,  etc.  Generally  the  upper  workings  do  not  pay,  90  per  cent,  of  the  gold  being 
obtained  from  near  the  bed-rock  ;  but  sometimes  the  upper  horizon  is  the  richest.  At  Patricksville,  gravel  is  overlaid  by  tufa ;  not  much  tnfaceons  cropping  at 
Lagrange.  Ancient  river  bed.  Deposit  in  patches  for  1  mile  wide  by  2J  miles  long. 

LYON  DRIFT  MINE. 
PLACERVILLE  DISTRICT,  EL  DORADO  COUNTY,  CALIFORNIA. 


I  "  Lava"  or  a  consolidated  sediment  of  volcanic  origin 60-130  feet. 

II  Mountain  gravel 0-50  feet. 

m  Granitic  sand,  in  places  consolidated 0-20  feet 

TV  Gravel Maximum,  20  feet ;  average,  3  j  feet. 

V  Bed-rock,  slate. 

Three  benches  of  ancient  river,  overlaid  with  volcanic  matter,  60  to  130  feet  wide,  are  here  traceable  for  3,000  feet. 

ORION  MINE. 
IOWA  HILL,  PLACER  COUNTY,  CALIFORNIA. 

I      Sand  and  fine  gravel ....    1  ( 

n      Coarser  blue  gravel >Maximnm,180feet;  average,  100  feet,  i  \    All  pays.  Bichest  near  bed-rock. 

III  Bed-rock,  black  slate,  rough. 

No  lava ;  no  quicksand.    Ancient  river  bed,  said  to  be  2,000  feet  wide,  traceable  2J  miles. 

VAN  EMMOXDS1  MINE. 

MICHIGAN  BLUFFS,  PLACER  COUNTY,  CALIFORNIA. 

• 

.  ,  _ 

I      Very  little  lava. 
II      Fine  gravel,  alternating  with  sand  strata ,  , 

HI      Blue  gravel I  :    All  pays;  but  white  gravel  nearest 

TTT    '  AVI  •,         ,,.»i  !•  Maximum,  50  feet ;  average,  30  feet,  •{  I          bed-rock  best 

IV  >>   Illtc  g!M\  el......     ....................... 

V      Bed-rock,  rough  slate )  ( 

Petrified  wood,  leaves  of  oak,  pine,  etc.,  found  in  sand  strata.   It  is  unusual  to  meet  white  gravel  beneath  the  blue. 

MORRIS  RAVINE  MINE. 
MORRIS  RAVINE  DISTRICT,  BUTTE  COUNTY.  CALIFORNIA. 

I      Hard,  solid  lava  cap  in  places. 
H      Fine  quartz  gravel ! , 

III  Kotten  bowlders i I  Maximum,  150  feet ;  aver- I  !    A  little  gold  throughout.  Blue  gravel 

.„      „,  I  age.  40  feet.  richest. 

IV  Bin-gravel 3-20feet..l 

V      Bed-rock,  chloride  and  clay  slates,  rough  and  decomposed. 
Pipe-clay  occurs  irregularly  throughout  deposit.     Quicksand  met  with. 

SPRING  VALLEY  MINE. 
CHEROKEE  DISTRICT.  BUTTE  COUNTY,  CALIFORNIA. 

-^TZ ~ |  .  ~  

I      Lava  cap  over  part  of  claim. 
II       Fine  quartz  gravel 25-150  feet.  ]  ] 

III  Rotten  lm«-l,l...  s  of  yellow  slat,,  mixe.l  with  quartz  gravel 5-15    feet,   l'  iva'a  vel'.g, ' '  •luo'feet.  [     I!"1  Pa-v  in  KI  and  IV  ™  ^d~r"^- 

IV  .  Blue  gravel 15-SO     feet.  ) 

V       lied  rock,  where  exposed,   described  as   '-b^^It"  like  the  cap,  probably 

inrtiunoi  jiiiii-.     Sarrouoiding  country  loi'lA  shite. 


\Vutei-  and  quiekikind  found  in  large  quantities  at  the  depth  of  300  feet.    Barren  pipe-clay,  25  to  150  feet  in  places,  as  a  rule  overlying  rich  gravel. 


14 


PRECIOUS  METALS. 


HUNGARIAN   HILL  MINE. 
PLTJMAS  COUNTY,  CALIFORNIA. 


I 

n 

III 


Soil 

Loose  gravel,  name  character  from  surface  to  bed-rock  

Generally  soft  slate  bed-rock;  in  places  hard  siliceous  slate.     Rough,  with 
projecting  points  in  some  places  rising  nearly  to  surface. 


|  , 

> Maximum,  110  feet;  average,  75  feet. 
) 


Gold  thronghont  gravel.    All  pays. 


Kiver  bed,  with  rim-rock  on  each  side,  250  feet  wide;  traceable,  3j  miles.    No  lava,  water,  or  quicksand. 

CARROLL  DRIFT  MINE. 
McADAU'S  CREEK  DISTRICT,  SISKIYOU  COUNTY,  CALIFORNIA. 


I 

II 
III 

IV 

V 

VI 

VII 


Loam ,4  feet, 

I  Loose  tailings ,  6  feet. 

Wash  gravel,  with  clay  and  sand j  10  feet. 

Compact  yellowish-white  clay  (water  level) j  18  inches  to  4  feet. 

Coarse  yellowish  gravel  (bulk  of  deposit) j 

Qnartzoso  matter J  3-6  inches. 

Greenish  gravel 12  feet 


j,  Maximum,  115 
feet ;  average 
73  feet. 

j 


vm   i  Bed-rock,  rotten  brown  slato  and  hard  fine-grained  blue  slate. 


None  barren,  lint  only  a  email  portion 
pays  for  drifting.  The  pay  streak 
is  200  feet  wide  and  length  of  claim. 


Good  pay. 

Best  pny  ou  bed-rock  and  in  bed-rock 
to  a  depth  of  2  feet. 


Bed  of  McAdam's  creek.    Mining  is  carried  on  over  a  length  of  34  miles  by  a  width  of  150  to  COO  feet. 

OAK  GROVE  DRIFT  MINE. 
McADAM  S  CREEK  DISTRICT,  SISKIYOU  COUNTY,  CALIFORNIA. 


I 

n 
in 

IV 

v 

VI 
VII 

vin 


Loam 4  feet. 

Loose  tailings 6  feet. 

Wash  gravel,  with  clay  and  sand !  10  feet. 


18  inches  to  4  feet. 


Compact  yellowish  clay  (water  level) 

Coarse  yellow  gravel 

Qnartzoso  matter 4  to  fl  inches. 

Yellow  gravel 

Bed-rock,  brown  slate,  ridgy  and  seamy  in  places;  in  others  soft  and  open. 


Average,  63  feet. 


None  of  the  gravel  is  barren. 


Good  pay. 

The  best  pay  is  1  to  3  feet  on  bed-rock 
and  1  to  S 'feet  iu  bed-rook. 


PACIFIC  MINE. 

HUMBUG  DISTRICT,  SISKIYOU  COUNTY,  CALIFORNIA. 


n 

m 

IV 

v 


Loose  wash  gravel 

Coarse  yellow  gravel,  containing  many  large  bowlders 

Fine  sand 

Yellow  gravel 


20  feet. 
Dark  yellow  gravel [l  foot. 


5  feet 
8  feet, 
0  Inches  to  2  feet.  (  Maximum,  50  feet; 


average,  45  feet. 


VI   |  Bine  gravel 8  inches  to  10  feet.  . 

VII    i  Bed-rock,  bine  slate. 


Contains  but  little  gold. 


None  barren. 


>  Best  pay. 


River  bed  traced  for  1  mile,  average  50  feet  wide. 


BUNKER  HILL  MINE. 
DEL  NOKTE  COUNTY,  CALIFORNIA. 


I 

II 
HI 
IV 


Red  loam  mixed  with  fine  gravel 

Loose  gravel 

Gray  cement  streak,  60  feet  wide.     Large  bowlders  in  best  ground 

"Serpentine"  bed-rock  easily  piped,  having  bine  slate  under  it  (Leavens). 
Specimen  determined  as  highly  metamorphio  dioritic-looking  rock. 


15  feet.  1  Maximum  depth  of  bank,  125 


r  fep,t   I  feet;  average,  80  feet.  Maxi-     (None  of  the  gravel  is  barren,  bnt  the 
[   mum  depth  of  gravel,  50  feet;     [     richer  portion  is  near  bed-rock. 


20  feet,  j   average,  30  feet. 


Channel  one-half  to  three-quarters  of  a  mile,  150  feet  long ;  course  a  little  west  of  north. 

Large  deposits  of  copper  ores  have  been  found  in  the  auriferous  slate  series,  especially  in  Calaveras  county. 
Oopperopolis  is  the  principal  point,  but  there  are  also  deposits  at  Campo  Seco,  and  again  further  north  near  lone 
City.  Prospects  have  also  been  found  on  the  same  line  beyond  this  point.  The  or«s  are  native  copper  and  carbonates 
near  the  surface,  replaced  by  a  mixture  of  iron  and  copper  pyrite  below  the  water-line.  The  deposits  have  the  same 
dip  and  strike  as  the  inclosing  chloritic  slates.  Extensive  shipments  were  made  in  former  years. 

Mono  and  Iiiyo  counties,  though  politically  united  to  California,  considered  from  a  physico-geographical  point 
of  view,  form  a  portion  of  the  Great  Basin.  The  sedimentary  rocks  of  Mono  county  appear  to  be  Mesozoic,  but  the 
western  edge  of  the  great  Palaeozoic  area  which  covers  the  eastern  portion  of  the  Great  Basin  crosses  the  California, 
line  about  due  south  of  Columbus,  Nevada,  passing  near  Owen's  lake  and  then  diverging  to  the  southeast.  Great 
quantities  of  lava  are  met  with  in  both  counties,  as  throughout  the  Great  Basi*  The  deposits  of  these  counties  also 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  15 

bear  a  much  closer  resemblance  to  those  of  Nevada  thaii  to  those  of  central  California.  The  best  known  mining 
localities  are  Bodie,  Cerro  Gordo,  and  Panamint,  but  noHe  of  them  have  formed  the  subject  of  any  detailed  geological 
investigation. 

The  bullion  of  Bodie  is  usually  regarded  as  gold,  because  its  silver  contents  are  much  less  valuable  than  the 
accompanying  gold.  Keports  made  to  the  director  of  the  mint  for  the  year  1880  show  that  from  5  to  63  per  cent, 
of  the  value  of  the  bullion  produced  by  the  various  mines  was  silver,  which  also  formed  17.91  per  cent,  of  the  value 
of  the  total  product  ($3,063,699  13).  It  follows  that  from  45.7  to  96.5  per  cent,  of  the  weight  of  the  bullion  from 
different  mines  and  77.72  per  cent,  of  the  total  weight  was  silver.  In  1879,  when  a  smaller  portion  of  the  colorados 
were  worked  out,  silver  only  formed  65.2  per  cent,  of  the  entire  weight.  Bodie  metal  may  therefore  very  properly 
be  regarded  as  a  highly  dor£  silver  bullion,  similar  to  that  of  the  Comstock  lode,  and  as  essentially  different  from 
that  of  the  gravel  and  slate  region  ordinarily  known  as  the  gold  belt. 

The  Comstock  was  at  first  worked  for  gold.  The  Bulwer,  the  Syndicate,  and  the  Standard  Consolidated,  which 
show  but  little  silver,  are  on  top  of  a  hill  where  the  water-level  is  far  from  the  surface  and  the  quartz  is  reddened 
to  a  great  depth ;  the  Bodie  Consolidated,  Noonday,  and  others  are  at  lower  elevations.  The  sulphurets  of  these 
mines  are  not  oxidized,  and  the  bullion  shows  a  large  amount  of  silver. 

The  gangne  minerals  of  these  deposits  are  base  sulphurets,  quartz,  and  calc-spar.  They  are  inclosed  in  extremely 
decomposed  rock,  bearing  clear  signs  of  solfataric  action.  The  rock  is  so  highly  altered  that  tolerably  fresh 
specimens  are  not  obtainable  near  the  mines.  Slides  of  the  freshest  specimens  collected  are  not  decisive  as  to  the 
character  of  the  rock.  They  show  plagioclase,  and  apparently  some  orthoclase,  accompanied  by  mica  and  a  little 
hornblende;  the  ground  mass  also  contains  quartz.  Only  a  detailed  examination  in  the  field  will  decide  what  name 
the  rock  should  bear. 

The  mines  of  Cerro  Gordo  were  not  in  operation  during  the  census  year.  The  deposits,  which  at  one  time  were 
very  productive,  were  masses  of  argentiferous  lead  ores  occurring  in  limestone,  and  consisting  for  the  most  part  of 
carbonate,  sulphate,  and  other  decomposition  products  of  galena.  Schists  and  slates  were  also  met  with  in  the  mines,  ;is 
well  as  a  granite-porphyry.  This  is  said  to  occur  as  a  dike  in  the  Union  mine  and  elsewhere,  and  is  locally  called  syenite, 
though  it  is  qtiartzose  and  micaceous.  Panamint  was  for  a  short  time  a  very  flourishing  camp,  its  prosperity 
being  derived  from  veins  in  limestone  carrying  chiefly  argentiferous  gray  copper  ore  or  freibergite,  associated  with 
galena  and  zincblende.  Mining  is  still  being  carried  on,  but  the  richer  deposits  were  soon  worked  out.  The  age  of 
the  limestones  of  Cerro  Gordo  and  Panamint  is  unknown.  Both  districts  lie  near  the  contact  between  the  Palaeozoic 
and  the  Mesozoic,  and  may  belong  to  either;  but  limestones  are  exceptional  in  the  Trias  and  Jura  of  the  Sierra  region, 
while  they  predominate  in  the  Palaeozoic  area. 

Gold  has  been  found  at  a  great  number  of  points  in  the  Coast  ranges  proper  and  in  the  western  ranges  of 
southern  California.  No  doubt  large  individual  profits  have  been  made  at  certain  localities,  and  it  is  by  no  means 
impossible  that  as  good  or  better  veins  than  those  found  await  discovery.  It  is  scarcely  likely,  however,  that  after 
thirty  years  of  skillful  prospecting  any  important  gold-mining  region  has  escaped  observation.  A  few  years  since 
great  hopes  were  raised  by  the  prospects  on*  veins  in  the  slates  and  on  the  contact  between  slates  and  granite  in 
the  Julian  and  Banner  districts  near  San  Diego,  but  they  have  fallen  short  of  the  expectations  excited. 

'  The  so-called  Gold  Bluffs  along  the  coast  of  the  northern  counties,  especially  near  the  mouth  of  the  Klamath 
river,  are  bluffs  which  contain  extremely  small  quantities  of  gold,  and  seem  to  be  beds  of  detritus  left  by  the 
shifting  of  the  river  channels.  The  sea  encroaches  upon  them,  and  when  the  surf  strikes  the  beach  in  certain 
directions  and  with  a  certain  strength  the  gold  is  concentrated  in  comparatively  rich  sands,  which  are  gathered 
and  treated  in  apparatus  of  various  designs  by  amalgamation. 

The  only  quicksilver  ore  of  great  importance  is  cinnabar,  although  metacinnabarite,  the  black  sulphide,  is 
rather  abundant  in  a  few  mines,  and  metallic  quicksilver  sometimes  accompanies  the  deposits  of  its  compounds. 
The  metaoinnabarite  described  by  Dr.  G.  E.  Moore  was  amorphous,  but  according  to  Mr.  Goodyear  it  also  occurs 
as  minute  crystals.  Cinnabar  is  found  in  a  great  number  of  localities  in  the  Coast  ranges  for  100  or  150  miles  north 
and  south  of  San  Francisco,  always,  so  far  as  known,  ill  metamorphic  rocks  of  Cretaceous  age.  The  character  of 
the  metamorphism  is  generally  peculiar,  and  the  so-called  quicksilver  rock  is  readily  recognizable.  It  is  a  silicitted 
chert  like  material,  often  reddened  by  iron  oxide,  and  usually  accompanied  by  serpentine  or  serpeutiuoid  matter. 
In  almost  all  cases  pyrite  or  marcasite  and  bituminous  matter  accompany  the  cinnabar,  and  mispickel  and  copper 
pyrite  are  reported  in  a  few  instances.  At  Sulphur  Banks,  on  Clear  lake,  native  sulphur  occurs  in  great  quantities 
with  the  quicksilver  ore,  and  native  gold  has  been  found  in  water- worn  masses  of  cinnabar  not  far  from  the  same 
locality.  The  converse  occurrence  of  cinnabar  in  two  of  the  quartz  veins  of  the  Sierra  gold  belt  has  already  been 
noticed.  Stibnite  is  reported  as  occurring  with  cinnabar  at  the  Lake  mine  near  Knoxville.  The  usual  gangue 
minerals  are  quartz,  calcite,  and  magnesite. 

Cinnabar  does  not  occur  in  well-marked  veins,  but  generally  in  irregular  bodies  distributed  through  the  rock. 
In  the  New  Almadeii  mine,  which  has  been  much  more  extensively  woi  ked  than  any  other  in  the  state,  these  bodies 
appear,  from  a  model  constructed  by  the  owners,  to  lie  on  a  curved  surface,  indicating  a  geometrical  relation  between 
the  positions  of  the  several  ore-bodies,  though  an  obscure  one.  At  this  mine  the  masses  of  ore  are  usually  connected 
by  tiny  seams  of  the  same  material.  There  is  a  strong  similarity  between  this  mode  of  occurrence  and  that  of 
many  lead  ore  deposits  in  limestone,  and  it  may  be  that  the  problem  of  their  tme  character  is  the  same. 


16 


PRECIOUS  METALS. 


The  quicksilver  country  north  of  San  Francisco  is  a  volcanic  region,  while  to  the  south  volcanic  rocks  are 
subordinate  in  some  localities  and  wanting  in  others.  To  the  south,  too,  there  is  no  indication  of  any  recent 
deposition  of  the  ore,  while  to  the  north  deposition  is  still  actually  in  progress.  No  general  inference  as  to  the 
genesis  or  the  age  of  the  deposits  can  therefore  be  drawn  without  further  investigation,  while  the  great  similarity 
in  the  association  of  minerals  suggests  a  similar  origin  for  most  of  them. 

The  Sulphur  Banks,  on  Clear  lake,  forms  the  subject  of  a  recent  paper  by  Professors  Le  Conte  and  Rising,  (a) 
At  that  point  cinnabar  with  pyrite  and  some  bituminous  matter,  as  well  as  free  sulphur,  is  now  being  deposited. 
The  hot  waters  rising  to  the  surface  are  charged  with  sulphides  of  ammonium  and  of  the  fixed  alkalies,  and  appear 
to  carry  in  solution  cinnabar  and  pyrite,  which  are  deposited,  in  the  opinion  of  the  authors,  by  reduction  of 
temperature  and  pressure,  probably  assisted  by  neutralization  through  the  percolation  of  free  sulphuric  acid  from 
the  surface.  The  deposition  of  sulphur  is  a  surface  phenomenon.  It  may  also  have  attended  the  formation  of  the 
deposits  to  the  south  of  San  Francisco  and  Lave  been  subsequently  removed  by  erosion. 

The  only  Californiuii  coal-fields  of  great  importance  are  those  near  Monte  Diablo,  which  occur  in  sandstones  of 
the  Upper  Cretaceous  or  Tejon  group.  According  to  Professor  S.  F.  Peckhain's  examination,  (/>)  these  coals  carry 
from  5  to  11  per  cent,  of  ash,  4i  to  5.J  per  cent,  of  sulphur,  and  from  11£  to  13  per  cent,  of  water.  The  refuse  dumps 
of  these  mines  frequently  take  fire  spontaneously  from  the  oxidation  of  pyrite.  Coal  of  the  same  age  occurs  under 
less  favorable  conditions  at  Corral  Hollow,  in  the  Monte  Diablo  range.  Seams  are  fonnd  here  and  there  all  along 
the  Coast  ranges,  but  they  are  usually  thin,  and  even  when  of  a  workable  thickness  are  so  faulted  and  broken  as 
to  be  of  small  value. 

Lignite  of  Pliocene  age  is  found  at  lone  valley,  Amador  county,  and  is  used  along  the  line  of  the  railroad  to 
some  extent  at  Dog  creek,  near  the  Truckee  river. 

In  southern  California  there  are  vast  quantities  of  bitumen,  from  which  asphalt  and  a  certain  quantity  of 
illuminating  oils  are  obtained.  The  bitumen  occurs  in  shales  of  the  Miocene,  which  are  in  large  part  too  much 
disturbed  to  permit  of  the  accumulation  of  pressure  necessary  to  induce  flowing  wells.  Many  of  these  bitumens, 
though  thin  as  they  issue  from  the  gronud,  oxidize  and  are  converted  into  hard  asphalts.  According  to  Professor 
Peckham,  the  California  bitumens  are  composed  of  a  different  series  of  hydrocarbons  from  those  which  make  up 
the  petroleums  of  Pennsylvania. 

AMADOR  COUNTY. 

This  county  lies  directly  across  the  main  gold  belt.  Quartz  mining  takes  the  first  rank,  though  there  are  gravel 
deposits,  and  hydraulic  mining  is  carried  on  to  a  considerable  extent.  The  gold  in  the  veins  is  associated  with  iron 
and  copper  pyrite,  marcasite,  mispickel,  and  small  quantities  of  galena.  The  gangue  is  chiefly  quartz,  but  some 
calcite  is  occasionally  found  in  the  veins.  The  country  rocks  are  slate  and  granite,  the  former  being  predominant, 
but  a  greenstone  also  occurs,  which,  though  much  decomposed,  is  probably  a  diabase  or  proterobase.  The  mother 
lode  has  been  traced  with  certainty  from  Mariposa  to  about  the  center  of  Ainador.  Copper  is  found  in  the  western 
portion  of  the  county,  but  it  is  not  at  present  worked,  and  a  lignite  o&curs  at  lone  City  which  is  of  considerable 
local  importance. 

AMAUOK.  « 

[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 


Ore  anil  gangue. 


WALLS. 


Foot. 


Hanging. 


AMADOU  CITY. 

Keystone (Gold,  chalcopyrite,  galena),  pyrite  and  quartz  . .' Proterobase  (?)  * Proturobase  (?)*. 

JACKSON. 
Monte  Richard 


(Gold),  iron-stained  quartz (Greenstone  or  augite-por-     Proterobase 

phyry,  called  granite.) 


Oru-ida (Gold,  galena,  chalcopvrite,  ami  marcasite).  pj rite     Grcenot  one,  probably  an  au-    do 

and  quartz.  gite-porphyry. 

Zcile i  (Gold,  pyrite,  rarely  galena  and  cbalcopyrite,  quartz) .    (?) ,  Qoartzite 

PLYMOUTH. 

I'lu-itic      Mining     Company     (Gold),  indeterminable  black  sulphurets  and  quartz 

(Kmpire,  etc.,  mines). 

SUTTEH  CREEK. 

Consolidated  Amador (Gold,  galena,  chalcopyrite,  mispickel),  pyrite  and  I  (Clay  mic:v  elate) (Talcose  slate) . 

quartz. 

VOLCANO. 
Madeira (Gold),  galena,  calcite,  and  quartz. 


Character  of 
deposit. 


Vein. 

Vein. 
Do. 

Do. 

Vein. 

Vein. 


*  Examined  microscopically. 
a  American  Journal,  vol.  2-4,  v>.  2:1,  1882.  l>  Ceoloyical  Surrey  of  California:  Geology,  II,  p.  44. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


17 


BUTTE  COUNTY. 

A  large  part  of  Butte  county  lies  in  the  Great  Valley,  and  produces  no  gold;  but  the  eastern  portion  contains 
extensive  gravel  deposits,  which  are  continuations  of  those  of  Plumas  and  Yuba.  Much  of  the  gravel  is  covered 
by  a  cap  of  basalt,  and  the  bed-rock  is,  in  all  the  cases  reported,  sandstone  or  metamorphic  slate. 

BUTTE. 
[NOTE.— Determinations  in  parentheses  are  giren  on  the  authority  of  the  experts.] 


w^ 

LL6.  ' 

Character  of 

Mine. 

Foot. 

Hanging. 

deposit. 

CEXTERVILLE. 

Basalt  cap*  

Placer. 

CHEROKEE. 

(Gold  gravel)         ...        .... 

Altered  diabase*  

Do. 

'  Examined  microscopically. 


CALAVERAS  COUNTY. 

Both  quartz  and  gravel  mining  are  actively  pursued  in  this  county,  which  lies  across  the  gold  belt.  The 
auriferous  quartz  carries  iron  and  copper  pyrites,  mispickel,  galena,  and  zincblende.  The  wall  rocks  in  all  the  cases 
reported  are  metamorphic.  The  mother  lode  crosses  this  county.  The  gravel  is  of  the  ordinary  character,  and, 
as  usual,  is  accompanied  by  more  or  less  basaltic  lava.  Copper  deposits  occur  below  or  to  the  west  of  the  gold 
belt  at  and  near  Copperopolis. 

CALAVEKAS. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mines. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

AXGEL'S. 

Vein. 
Do. 

MOKELUMNE  HILL. 

Gwin 

(Gold,  mispickel,  zincblende),  pyrite,  chalcopyrite, 
and  quartz. 

(Black  slate) 

(Black  slate) 

DEL  NORTE  COUNTY. 

Auriferous  gravels  are  the  chief  metalliferous  deposits  of  this  county,  the  bed-rock  consisting  of  slate  and 
other  sedimentary  strata.    Beach  sands  are  also  worked  to  a  small  extent  on  the  coast. 


DEL  NORTE. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  expert.] 


WA 

LLS. 

Character  o 

Foot. 

Hanging. 

deposit. 

Bunker  Hill 

(Goldgravel)  

Placer 

China  Creek            

.do  

Do. 

Del  Norte  

....do  

Slate        

Do 

Happy  Camp  

....do  

do  

Do 

Muc-a-muc  

....do  

Shale  

» 

Do. 

Wingate  

....do  

Slate  

Do. 

VOL  13 2 


18 


PRECIOUS  METALS. 


EL  DORADO  COUNTY. 

El  Dorado  lies  across  the  gold  belt,  and  contains  a  great  deal  of  gold  quartz,  while  the  placers  are  comparatively 
insignificant.  Some  of  them,  however,  buried  under  heavy  caps  of  lava,  are  profitably  worked  by  drifting.  The 
gold  quartz  carries  the  usual  sulphurets,  pyrites,  mispickel,  and  zincblende.  The  country  rock  is  chiefly  slate. 
Copper  ores  also  occur  in  the  western  part  of  the  county. 

EL  DORADO. 
[NOTB. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

FLACEBVILLB. 

(Gold  gravel) 

Slate 

Lava  cap,  basalt,  pumice*  .. 

Placer. 
Vein. 
Do. 

Gold,  pyrite,   mispickel,  quartz,  (zincblende  and  ga- 
lena). 

(Slate)  ...             

(Slate)     . 

'  Examined  microscopically. 


FRESNO  COUNTY. 

Fresno  extends  from  the  crest  of  the  Sierra  to  the  Coast  ranges.  It  lies  to  the  south  of  the  main  gold  belt,  but 
'contains  a  few  gold  quartz  veins  in  the  Potter  ridge  district  and  elsewhere,  carrying  the  usual  sulphurets,  and 
being  inclosed  in  slates.  At  the  western  edge  of  the  county  is  the  famous  New  Idria  quicksilver  mine,  in  which 
cinnabar  is  accompanied  by  pyrite  and  bituminous  matter.  According  to  Mr.  Goodyear,  the  ore  does  not  occur  in 
a  vein,  at  least  of  the  typical  character,  but  in  irregular  bodies,  distributed  in  metamorphic  sandstone  and  shale. 

FRESNO. 
[NoTK. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine 

WA 

I.LB. 

Character  of 

Foot. 

Hanging. 

deposit. 

• 

SAN  CARLOS. 

New  Idria  

Cinnabar,  (pyrite,  chalcopyrite,  and  bitumen)     

Vein 

POTTEB  BIDGR. 

Fresno  Enterprise  

(Gold,  sulphurets,  and  quartz)  

(Slate)  

(Slate) 

Do 

HUMBOLDT  COUNTY. 


There  is  no  gold  quartz  mining  in  Humboldt,  and  the  placer  mines  are  not  extensive,  compared  with  those  of 
the  central  counties.  The  gravels  appear  to  represent  modern  river  bars  of  the  Klamath,  along  the  banks  of  which 
they  are  -found,  in  some  cases,  however,  at  a  very  considerable  elevation  above  the  present  stream.  As  in  Del 
Norte,  there  are  auriferous  beach  sands,  which  can  be  worked  with  profit  when  certain  combinations  of  wind  and 
waves  have  effected  a  preliminary  concentration  of  the  auriferous  material. 


INYO  COUNTY. 

The  most  important  mines  in  this  county  carry  argentiferous  lead  ores  with  calcareous  gaugue.  They  occur 
either  in  limestone  or  in  limestone  associated  with  granite  and  schist.  The  deposits  are  chimneys,  or  bodies  of  an 
irregular  form,  such  as  lead  ores  frequently  assume  elsewhere.  Copper  ores,  associated  with  those  of  lead,  also 
occur.  Where  copper  is  the  principal  constituent  the  gangue  is  usually  siliceous.  The  copper  veins  occur  in 
limestone  or  in  granite,  or  on  the  contact  between  the  two.  The  lead  ores  are  galena,  cerussite,  anglesite,  and 
probably  lead  ocher,  accompanied  by  argentite  and  other  silver  minerals.  The  copper  ores  are  chalcopyrite, 
stromeyerite,  tetrahedrite,  bornite,  and  carbonates.  They  are  usually  argentiferous.  In  addition  to  the  gangue 
minerals  mentioned,  fluorite  is  found  in  the  Defiance  mine,  in  a  silver-lead  deposit  between  granite  and  limestone. 
There  are  also  gold-quartz  veins  in  granite  in  the  county,  and  some  small  gold  placers.  At  the  Lee  mine  argentite 
and  horn-silver  are  reported  as  occurring  in  limestone. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


19 


INTO. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot 

Hanging. 

CEBBO  GOBDO. 

(White  limestone)  

Schist  (white  limestone). 
Marble. 
do. 

Vein. 

Vein. 

Do. 
Do. 

Do. 
Bedded  vein. 

Vein. 

Bedded  rein. 

Vein. 

Flat  vein. 

Vein  ;    also   small 
placer. 

Deposits. 

Marble                             

do                       

....do  

)                                                J 

i  Granite,  porphyry  dike  *.  > 

(Granite)                .  . 

CO8O. 

Galena,  cenissite,  chalcopyrlte,  malachite,  fluorspar, 
calcite,  and  pyrite. 

Siliceous  limestone  

do 

(Granite)  

New  Coso  Company  (includ- 
ing Lucky  Jim  and  Christ- 
mas Gift). 

Limestone  (containing  bari- 
nm). 

(Granite)  

(Granite)     

Limestone  and  schist  

KEARSABGE. 

Cernssite,    micaceous   iron,  limonite,    (tetrahedrite, 
cerargyrite,  and  argentit*),  qnartz. 

Stromeyerite,  (tetrahedrite,  galena,  pyrite,  and  zinc- 
blende),  quartz. 

(Cernssite,  carrying  gold  and  silver,  with  arsenic  and 
antimony  ;  calcite,  iron  oxide,  and  manganese  min- 
erals.) 

(Cernssite,  galena,   bornite,   malachite,  pyrite,  and 
quartz.) 

Granite* 

Granite*           

PANAMCTT. 

(White  limestone) 

LOOKOUT. 

Modoc  Consolidated 

KUSe. 

FISH  BPRIMGS. 

Golden  Wreath, 

Granite 

Granite 

(Gold  quartz) 

(Granite)          

(Granite) 

Lee  

(Limestone)  ... 

(Limestone)  

*  Examined  microscopically. 


KERN  COUNTY. 


Kern  county  lies  south  of  the  main  gold  belt ;'  it  nevertheless  contains  some  gold-quartz  veins  in  its  northeastern 
portion,  in  the  Sierra  range,  as  well  as  some  shallow  placer  gravels. 


LAKE  COUNTY. 

The  only  important  mineral  di-posits  of  Lake  county  are  those  of  quicksilver,  which  occur  at  a  number  of  points 
in  considerable  quantities,  accompanied  by  pyrite,  sulphur,  bituminous  matter,  and  quartz.  The  inclosing  rocks  are 
metamorphic.  The  deposits  are  associated  in  some  cases  with  basalt. 


LAKE. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

Vein. 
Irregular  deposit. 

EAST  LAKE. 

Sulphur  Banks 

(Cinnabar,  native  sulphur,  bitumen,  pyrite,  borax, 
alum,  and  quartz.) 

Sandstone  and  basalt  

Sandstone  and  basalt.  

20 


PRECIOUS  METALS. 


LASSEN  COUNTY. 

This  county  contains  gold-quartz  mines.  The  veins  are  associated  with  rocks  which  are  in  part  raetamorphic 
and  probably  also  in  part  eruptive,  but  the  specimens  in  the  collection  are  so  decomposed  as  to  be  indeterminable. 
Enormous  quantities  of  lava  cover  much  ground  in  this  part  of  the  state  that  would  probably  otherwise  be 
remunerative. 

LASSEN. 
[Nora. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

IIAYDKH  HILL. 

Vein. 
Do. 

Ho                  ,               ... 

do                      

..    do  -•  

LOS  ANGELES  COUNTY. 


There  is  some  silver  mining  in  this  county.  Antimonial  silver  ores  and  argentiferous  galena  occur  with  pyrite, 
copper  ores,  and  quartz  inclosed  between  wall  rocks  which  are  chiefly  sedimentary,  but  probably  in  part  eruptive. 
Asphalt,  petroleum,  and  coal,  as  well  as  salt,  are  also  found  in  the  county. 


LOS  ANGELES. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

SILVERADO. 
Bine  Light  

Galena,  pyrite,  and  quartz..  -  

Limestone  and  quart  zite  
Quartzite 

Limestone  and  quart  zite  .... 
Shale. 

Probably  diorite. 

Vein. 

Galena,   zincblende,  pyrite,  (antimony  and   copper 
stains). 

do 

Phojnix  .        .         

MARIPOSA  COUNTY. 

This  is  the  most  southerly  county  on  the  gold  belt,  and  contains  many  gold-quartz  veins  inclosed  in  slate. 
Argentite,  proustite,  and  (it  is  said)  silver  telluride  are  also  found.  The  southern  end  of  the  mother  lode  is  in  this 
county  on  the  famous  "Mariposa  estate". 

MABIPOSA. 

[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


WA 

.L8. 

Character  of 

Foot. 

Hanging. 

deposit. 

MAHIPOSA. 
Hiti  

(Free  gold,  galena,  copper  pyrite,  occasionally  gold; 

Vein 

'  BEBASTAPOL. 

Modesta  

pyrite,  zincblende  quartz,  telluride  ore.) 

Coe  

{  Slate) 

Vein 

NAPA  COUNTY. 

In  this  as  in  the  adjoining  county,  Lake,  the  principal  useful  mineral  found  Is  cinnabar,  which  occurs  in  the 
usual  serpentinoid  and  arenaceous  metamorphic  strata.  The  Kedington  mine  is  one  of  the  most  important 
quicksilver  producers  in  the  state. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


21- 


NAP  A. 

[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 

• 
Or*  and  gauguo. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

OAT  HILL. 

Cinnabar,  with  sandstone  and  clay,  (bituminous  mat- 
ter). 

Cinnabar,     metacinnabarite,     marcasite,     bitumen, 
quartz,  (mispickel). 

Sandstone  

Vein. 
Irregular  bodies. 

Schist       

MONO  COUNTY. 

This  county  seems  to  contain  two  classes  of  deposits.  The  highly  dore"  silver,  or  low-grade  gold  of  Bodie,  is 
found  in  eruptive  rocks  of  as  yet  undetermined  character.  A  portion  of  the  gold  is  free,  but  a  large  part  of  it  is 
associated  with  complex  silver  sulphides,  accompanied  by  quartz  and  calcite  as  gangue  minerals.  The  other  districts 
are  granitic  and  carry  chalcopyrite,  copper  glance,  and  carbonates,  with  galena,  zincblende,  argentite,  and  other 
silver  minerals. 

MOM). 
[NOTB.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

BLIXl)  SPRING. 

Copper  glance,   chalcopVrite,   zincblende,  probably 
tetrahedrite,  chrysocolla,  (partzite,  malachite,  clay, 
and  quartz). 

Copper  glance,  chrysocolla,  copper  carbonates,  limo- 
nite  (partzite  and  malachite),  with  earthy  and  (de- 
composed granitic  gangne). 

Copper  glance,  chrysocolla,  copper  carbonates,  (ga- 
lena and  horn-silver). 

Granite  

Vein. 
Do. 

Vein. 
Do. 
Do. 
Do. 

Do. 
Do. 
Do. 
Do. 
Do. 
Do. 
Do. 

Vein. 
Do. 

Vein. 
Do. 

do      

do 

Modoc             

ItODIK. 

do  

Bulwer    

(Quartzose  and  feldspatuic  vein  matter  carrying  gold 
and  silver.) 

McCliuton 

do                                

Oro 

Standard  Consolidated 

(Gold  and  silver  bearing  quartz)  

do 

do             

(Gold  silver  quartz  and  feldspathic  matter)  

(Volcanic)     

(Volcanic)  

HOMKR. 

Maybell      

(Gold,  silver,  iron  pyrite,  galena,  and  quartz)  

do 

Granite 

1NU1AX. 

^Granite  and  porphyry)  
do 

(Granite  and  porphyry)  
do 

Galena,  zincblende,  native  silver,  tetrahedrite,  (pyrar- 
gyrite,  pyrite,  and  quartz). 

NEVADA  COUNTY. 

Nevada  has  always  been  one  of  the  most  productive  counties  in  the  state,  both  the  quartz  and  the  placer 
mines  yielding  very  large  amounts.  The  quartz  mines  are  for  the  most  part  in  the  slates  characteristic  of  the  main 
gold  belt,  but  some  of  them  are  in  granite,  and  some  of  them  are  on  the  contact  between  gran-ite  and  slate.  The 
gold  is  accompanied  by  iron  and  copper  pyrites,  mispickel,  galena,  and  zincblende.  As  elsewhere  in  the  gold  belt, 
the  proportion  of  silver  is  extremely  small,  even  by  weight.  Though  the  larger  part  of  the  gold  is  free,  the  sulphurets 
are  ordinarily  much  richer  than  the  quartz  taken  as  a  whole,  and  it  usually  pays  to  concentrate  them  and  subject 
them  to  the  Plattner  chloridation  process.  The  placer  deposits  are  in  part  covered  by  volcanic  rocks,  chiefly  basalt. 
The  cap  over  a  large  area,  however,  is  not  so  deep  as  to  prevent  the  gravel  from  being  worked,  as  it  does  to  a 
considerable  extent  in  the  counties  further  north,  while  the  amount  of  volcauic  material  has  been  sufficient  to  protect 
the  gravel  from  extensive  erosion.  One  of  the  great  Tertiary  rivers  flowed  through  this  county  in  a  southwesterly 
direction  and  gave  rise  to  the  large  gravel  accumulations. 


22 


PRECIOUS  METALS. 


NEVADA. 
[Nora.— Determinations  in  parentheses  are  given  on  the  authority  of  the  exports.] 


Mine. 

Ore  and  gangne. 

WALLS. 

• 

Character  of 
deposit: 

Foot. 

Hanging. 

GRASS  VALLEY. 

Idaho  ..  . 

Free  gold,  galena,  iron  and  copper  pyrites,  and  some- 
times zincblende,  quartz. 

Gold,   pyrite,   zincblende,    galena,  quartz,   (copper 
pyrite). 

(Gold),  pyrite,  (zincblende,  galena,  iron,  and  copper 
pyrito),  quartz. 

Pyrite  and  quartz. 

(Gold),  pyrite,   (galena,    copper,   and   iron   pyrite), 
quartz. 

(Gold,  iron,  nnd  copper  pyrito,  galena,  zincblende,  and 
quartz.) 

Magnesian       metamorphic 
rock. 

Slate  

Magnesian       metamorphic 
rock. 

Slate 

Vein. 
Do. 
Do. 

Vein. 
Do. 

New  York 

NEVADA  CITY. 

Merrifleld 

Granite         .                ... 

Granite                 .     . 

do 

PLACER   COUNTY. 


Placer  lies  directly  across  the  gold  belt,  and  is  one  of  the  principal  producing  counties.  The  gold-quartz  veins 
occur  for  most  part  in  slates,  though  some  are  found  in  granite,  and  they  present  the  usual  association  of  sulphurets. 
The  auriferous  gravels  have  been  sufficiently  protected  by  volcanic  material  to  escape  radical  erosion  without  being 
so  deeply  covered  as  to  be  inaccessible.  Iron-ore  deposits  are  abundant. 


PLACER. 
[NOTE. — Determinations  in  parentheses  are  given  on  authority  of  the  experts.) 


Mine. 

Ore  and  gaiigne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

COLKAX. 
Rising  Sun  

(Granite) 

(Granite) 

Vein. 

PLTJMAS   COUNTY. 

The  gold  belt  in  the  latitude  of  Plurnas  county  is  not  so  sharply  denned  as  further  south.  Deposits  of  the 
precious  metal,  however,  are  abundant,  both  as  veins  and  in  gravel.  The  association  of  sulphurets  accompanying 
the  gold  is  the  same  as  in  Nevada  county.  The  wall  rocks  are  either  slates  and  other  metamorphic  rocks  or  granite 
or  both.  The  slaties  are  sometimes  so  intersected  by  auriferous  quartz  as  to  give  the  veins  a  reticulated  character. 
Although  the  production  of  the  placer  mines  is  considerable,  a  large  part  of  the  gravel  is  supposed  to  be  inaccessible 
through  the  presense  of  heavy  overlying  sheets  of  basalt. 

PLTJMAS. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 

Ore  and  gancue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

CHEROKEE. 

Plnmas  Eureka  

Metamorphic  diorite  *  

Slate 

Metamorphic  diorite  *  
Slate 

Vein. 
Reticulated  vein. 

Veto. 
Do. 
Do. 
Do. 

Vein. 
Placer. 

GENEBKE  VALLEY. 

Gcncsee  

(Gold)  ,  slate  and  quartz  

INDIAN  VALLEY. 

Gold  Stripe  

(Gold  generally  free  from  sulphurets)   qnartz 

(Slate) 

Green  Mountain  

(Gold,  pyrite),  quartz  

(Decomposed  granite)  
(Granite)  
Slate 

(Decomposed  granite)  
(Slate)  

Slate 

Monitor  

Dumas  National  

(Quartz),  pyrite  and  mispickel  

BENECA. 
Savcrcool  

(Gold),  pyrito  sandstone,  and  quartz  

(Clay  slate) 

Sunnyside  Gravel  

(Auriferous  gravels)  

P 

*  Examined  microscopically 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


23 


SACRAMENTO  COUNTY. 

The  <ieposits  of  Sacramento  county  are  mainly  gravels,  and  are  confined  to  its  eastern  and  northern  borders, 
where  it  adjoins  Placer,  El  Dorado,  and  Amador.  These  gravels  are  in  fact  the  western  extremities  of  the  extensive 
fields  occurring  in  the  more  eastern  counties.  A  larger  product  is  usually  accredited  to  the  county  than  it 
actually  yields,  much  bullion  being  shipped  within  its  borders  which  is  produced  elsewhere.  This  is  a  consequence 
of  the  commercial  importance  of  several  towns  of  the  county,  among  which  is  the  capital  of  thfe  state. 

.  SAN  BERNARDINO  COUNTY. 

There  are  veins  in  granite  in  this  county  which  carry  gold,  copper,  silver,  and  lead.  There  are  also  copper 
veins  in  limestone.  Tin  ore  deposits  are  found  at  Temescal,  where  the  ore  is  of  an  unusual  character,  but  these 
are  not  now  worked.  Platinum  sand  is  said  to  occur. 

SAN  BERNARDINO. 
[NOTE.— Determinations  in  parentheses  arc  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

CLARK. 

Ally... 

(Argentiferous),  stromeyerite  ,.. 

Limestone  

Vein. 
Do. 

% 

Vein.^ 
Probably  vein. 

Vein. 

(Argentiferous),    stromeyerite,    copper    carbonates, 
(limestone). 

(Argentiferous),    stromeyerite,    copper   carbonates, 
(limestone). 

Limestone,   probably  dolo- 
mitic. 

do    

Limestone,    probably  dolo- 
mitic. 

da 

(Granite) 

Liule  Bullock  

DET  LAKE. 
Desert  Chief  

(Granite) 

BILVEH  MOUNTAIN. 

(Gold),  stromeyerite,  malachite,  lead,  and  quartz 

(Granite)  . 

(Granite) 

BAH  JAcnrro. 

Cassiterite  and  quartz. 
Granitic  or  dioritic  sand,  said  to  carry  platinum. 

SAN  DIEGO  COUNTY. 

There  are  some  gold-quartz  veins  in  San  Diego  occurring  in  metamorphic  rocks  and  granite.     Salt  also  forms 
one  of  the  resources  of  this  county. 

SAN  DIEGO. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 

Ore  and  gangue. 

Character  of 

Foot. 

Hanging. 

deposit 

BAKNKB. 
Hnbbard  

Gold,  sulphnrets  and  quartz 

Slate 

Slate 

Vein 

PDfECATB. 

Gold  State  ."  

Do 

CARGO  MBCHACHO. 

Madre,    Padre,    and    Cargo 

Do 

Muchacho  mines. 

SAN  LUIS  OBISPO  COUNTY. 

There  are  several  occurrences  of  cinnabar  in  metamorphic  rocks,  which  appear  to  be  similar  to  the  more  northern 
deposits  of  this  ore.    Chromic  iron  is  found  in  considerable  quantities. 


SAN  LUIS  OBISPO. 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

BAN  LUIS  OBISFO. 

Aagitic  porphyry. 
Metamorphic.* 

(Shale)         

Impregnation. 

do 

BAH  SIMEON. 

Pnlar  St*' 

Cinnabar. 

'  Microscopically  examined. 


24 


PRECIOUS  METALS. 


SANTA  BARBARA  COUNTY. 

No  important  deposits,  except  of  bitumens,  are  found  in  this  county. 

SANTA  BABBAEA. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Banging. 

6ANTA  ItARBAKA. 

- 

Impregnation. 

SANTA  CLARA  COUNTY. 


The  chief  mineral  resources  of  this  county  are  the  cinnabar  deposits  of  the  New  Almaden  and  Guadalupe 
mines.  They  form  irregular  deposits,  in  many  cases  connected  by  veinlets  of  ore.  The  cinnabar  is  accompanied 
by  pyrite,  calcite,  magnesite,  and  bitumen.  Dolomitic  limestone,  shale,  and  serpentine  are  the  inclosing  rocks. 


SANTA   CLAEA. 


WA 

uu. 

Character  of 

root 

Hanging. 

deposit. 

Vein. 

pyrite. 
Cinnabar  (and  calc-spar),  bitumen,  magnesite,  quartz 

and  dolomite. 

Do. 

SHASTA  COUNTY. 

There  are  veins  in  the  schists  and  granites  of  this  county  which  carry  silver  ores  and  gold  associated  with  iron 
and  copper  pyrite,  galena,  and  zincblende.  A  very  remarkable  occurrence  is  that  of  the  Mad  Ox  mine,  where 
native  gold  is  found  in  caleite.  The  deposit  is  reported  as  a  2£-foot  vein.  The  foot  wall  is  schist  and  the  hanging 
wall  a  siliceous  limestone.  Quartz  and  pyrite  also  occur  in  this  vein  as  gangue  minerals.  Shasta  contains  some 
gold-placer  mines. 

SHASTA. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

IKON  MOUNTAIN. 
Lost  Confidence  .'.  

(Silver  and  gold.)    The  silver  is  probably  present  as 
chloride,  limonite,  copper,  pyrito,  raarcasite  (argen- 
tite  j  the  pyrite  is  rich),  quartz. 

(Gold)  

Schist 

Schist 

Vein. 
Placer. 

Vein. 
Do. 

NEAR  ISO. 

Dry  Creek,  or  Hardscrahble  . 

F1TT8BUBUU. 

Potter  MiuingCo  

Slate  bed-rock  

Copper    oxide,    sulphide   and   carbonate,  limonite, 
pyrite,  (silver  and  zincblende)  . 

Galena,  pyrite,  quartz,  (chalcopyrite,  antimony,  ruby 
silver,  native  silver,  gold,  and  zincblende). 

Native  gold  in  calcite,  limonito,  quartz,  pyrito,  (sul- 
phurets  and  talcoso  schist). 

Slate  (porphyry  and  slate)  .  . 
(Granite) 

Slate  (porphyry  and  slate). 
(Granite) 

80DTH  FORK. 

Chicago  

WHISKY  CREBK. 

Mad  Ox  

Schist 

SIERRA  COUNTY. 


Sierra  county  lies  between  Nevada  and  Pluinas,  and  shares  the  geological  character  of  those  counties.  Both 
its  placer  and  quartz  mines  produce  largely,  but  present  no  characteristics  not  shared  by  those  of  the  adjoining 
regions. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


25 


SISKIYOU  COUNTY. 

Siskiyou  county  contains  gold-quartz  veins  occurring  in  inetamorphic  rocks  and  accompanied  by  pyrite, 
mispickel,  etc.  Greenstone  is  reported  as  the  hanging  wall  of  the  Black  Bear  and  the  Klamath,  but  no 
specimens  of  this  rock  have  been  received,  and  it  is  therefore  impossible  to  pronounce  with  certainty  as  to  its 
character.  The  principal  product  of  the  county,  however,  is  derived  from  the  placers,  many  of  which  are  worked 
as  drift  mines. 

SISKIYOT7. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.  ] 


WAI 

.L8. 

Character  of 

Foot 

Hanging. 

deposit. 

INDIAN  CEEKK. 

Bay  City 

Argillaceous  limestone  bed- 

Placer. 

do 

rock. 

Do. 

do                  .                     ... 

do               

Do. 

M'ADAMS  CBKKK. 
Carroll  Drift 

Placer. 

do                  

do  

Do. 

do                 .          

do  

Do. 

do                 ..              

Shale  bed-rock    

Do. 

do               

do  

Do. 

do                  .               

.do  

Do. 

Siwash 

do                  

...do  

Do. 

OBO  FIKO. 

Slate  bed-rock  

Placer. 

QUABTZ  VALLET. 

Brecciated      metamorphic 

Vein. 

BCIAD  VALLET. 

Fort  Gofif  Creek 

rock. 
Schist  bed-rock    

Placer. 

do                          

do  

Do. 

TREKA. 

Pellet  and  Trnitt 

Schist  bed-rock    

Da 

SOUTH  FOBK  SALMON. 
Black  Bear 

Vein. 

BAWTER'B  BAB. 
Klamath 

ite). 

Do. 

STANISLAUS  COUNTY. 

This  county  lies  to  the  southwest  of  Tuolumne  and  Calaveras.  The  mining  interests  are  not  large,  and  consist 
principally  of  placer  deposits  in  its  northeastern  portion,  near  the  boundaries  of  the  counties  just  mentioned.  The 
gravels  of  Stanislaus  form  an  extension  of  those  of  the  adjoining  counties. 

SONOMA  COUNTY. 

The  only  ores  found  are  those  of  quicksilver,  the  chief  mine  being  the  Great  Eastern.  As  usual,  the  ore  is 
associated  with  pyrite  and  bitumen,  the  accompanying  rocks  being  sandstone,  limestone,  and  a  rock  so  highly 
metamorphosed  as  to  resemble  basalt  until  seen  under  the  microscope. 

SONOMA. 

[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

% 

Character  of 

deposit. 

Foot. 

Hanging. 

GUERNEVILLB. 
Great  Eastern 

Sandstone  and  limestone  .  .  . 

Vein. 

*  Microscopically  examined. 


26 


PRECIOUS  METALS. 


TRINITY  COUNTY. 

Though  gold-quartz  veins  occur,  placers  form  the  principal  deposits  of  the  county.  The  bed-rock  in  all  the 
cases  reported  is  sedimentary,  and  is  usually  slate.  The  Johnson  mine  shows  beautiful  occurrences  of  radial 
marcaslte. 

TEINITT. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLB. 

Character  of 
deposit. 

Foot. 

Hanging. 

CASON  CREEK. 

(Auriferous 
(Anriferons 
(Auriferous 

(Auriferous 
do 

Schist  bed-rook  

Placer. 
Placer. 
Placer. 

Placer. 
Do. 
Do. 
Do. 
Do. 
Do. 
Do. 

DOUGLAS  CITT. 

INDIAN  CRKEK. 

Slate  

RED  HILL. 

gravel).....  .-  

Slate  

do 

Slate  . 

do 

do  

Trinity 

do   .    ... 

do  

do  

Slate  

Wiltshire  

..  do  

CDINABAB. 

Cinnabar  an 

Serpentine. 

TUOLUMNE  COUNTY. 

Tuolumne  ceunty  lies  across  the  main  gold  belt.  Though  placer  deposits  occur,  the  mineral  wealth  of  this 
county  is  chiefly  in  the  form  of  gold-quartz  veins,  which  are  found  both  in  the  slates  and  the  granite.  The  minerals 
accompanying  the  gold  appear  to  be  independent  of  this  difference  in  the  character  of  the  wall-rocks,  and  present 
the  usual  association  of  quartz  with  iron  and  copper  pyrites,  galena,  etc.  The  mother  lode  runs  entirely  across  this 
county. 

TtrOLTJMNE. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

CONF1BEXCK. 

Confidence  

(Granite) 

(Granite) 

Vein. 
Vein. 
Vein. 
Vein. 

JAME8TOWM. 
Harris  &Heslip  ;.. 

(Slate) 

(Slate)    

BONOBA. 
Golden  Gate  

(Gold,    galcaa,    chalcopyrite,    pyrite,    calcite,    and 
quartz.) 

(Slate) 

(Slate) 

BOULBBYVILLE. 
Sonlsliy  .         .......,.,.i 

(Granite) 

VENTURA  COUNTY. 
Bitumens  yielding  oil  and  sulphur  deposits  are  found  in  Ventura. 

YUBA  COUNTY. 

Though  there  are  quartz  veins  in  this  county,  the  principal  deposits  are  placers,  which,  though  they  were  among 
the  first  worked  in  the  state,  still  yield  largely.  Comparatively  little  of  the  gravel  is  covered  by  lava. 

OTHER  COUNTIES. 

Alpine,  Colusa,  Mendocino,  Merced,  Tehama,  and  Tulare  counties  all  produce  precious  metals,  though  not  in 
large  quantities,  and  very  little  is  known  of  the  details  of  their  occurrence,  but  there  is  nothing  to  lead  to  the 
supposition  that  the  character  of  the  deposits  differs  essentially  from  that  of  the  quartz  veins  and  placers  of  the 
better  known  regions  adjoining  them. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  27 

GEOLOGICAL  SKETCH  OF  OREGON  AND  WASHINGTON  TERRITORY. 

The  topography  »f  Oregon  and  Washington  territory  bears  a  general  resemblance  to  that  of  California.  Near 
the  coast  are  low  ranges,  separating  from  the  sea  a  long  valley,  to  the  east  of  which  rise  important  chains.  The 
mean  rainfall  in  the  western  portions  of  this  region  is  very  great,  and  much  country  is  covered  by  dense  forests. 
To  the  east  of  the  great  ranges  the  climate  and  physical  character  of  these  two  political  divisions  are  similar  to 
those  of  the  adjoining  territory  of  Idaho.  Both  Washington  territory  and  Oregon  produce  coal  in  important 
quantities,  but  the  precious-metal  production  of  the  more  northern  area  is  very  small,  while  Oregon  yields  above  a 
million  a  year  in  gold. 

Extremely  little  is  known  of  the  geology  of  these  areas,  which  have  been  'examined  almost  exclusively  with 
reference  to  their  bearing  on  doubtful  points  in  the  geology  of  regions  to  the  south  and  southeast.  '  Mr.  King,  in  his 
Systematic  Geology,  gives  the  main  facts  known  on  the  subject;  and  some  information  regarding  it  is  to  be  found 
in  the  Pacific  railroad  reports  and  in  the  American  Journal  of  Science. 

As  has  been  mentioned,  the  Sierra  Nevada  mountains  were  formed  during  a  great  post-Jurassic  upheaval.  The 
Cascade  range,  however,  is  more  recent,  although  from  a  topographical  point  of  view  it  might  be  regarded  as  a 
continuation  of  the  great  Sierra.  The  real  northern  representative  of  the  Sierra  is  the  Blue  Mountain  range  of  eastern 
Oregon,  for  both  are  due  to  the  same  orographical  cause.  The  coast  of  the  Pacific  ocean  of  the  Cretaceous  period, 
therefore,  bent  eastward  to  the  north  of  California,  and  followed  the  Blue  Mountain  range  northward.  The  Blue 
mountains  are  composed,  like  the  Sierra,  of  granite  and  metamorphic  strata,  and  in  the  latter  Mr.  King  found 
Triassic  fossils.  It  is  probable  that  nearly  or  quite  all  of  the  metamorphie  rocks  of  Oregon  east  of  the  Blue  range 
are  Triassic  or  Jurassic.  The  Cascade  range  contains  marine  upper-Cretaceous  beds,  (a)  but  so  far  as  is  known  none 
of  later  date,  and  it  was  probably  raised  above  water-level  at  the  close  of  the  Cretaceous.  It  was  certainly  uplifted 
before  the  Miocene,  for  during  this  epoch  a  fresh- water  lake  occupied  the  interval  between  it  and  the  Blue  mountains. 
West  of  the  Cascade  range,  and  near  the  coast  on  the  other  hand,  Cretaceous  and  Tertiary  strata  predominate  both 
in  Washington  territory  and  in  Oregon,  and  it  is  probable  that  the  coast  ranges  of  Washington  and  Oregon,  like 
those  of  California,  were  elevated  chiefly  by  a  post-Miocene  disturbance. 

Throughout  the  Miocene  immense  volumes  of  lava  reached  the  surface  in  Oregon  and  Washington  territory, 
and  the  area  occupied  by  it  perhaps  forms  the  largest  lava  field  in  the  world.  It  spared  an  irregular  belt  along  the 
coast  and  failed  to  cover  the  northeastern  corner  of  Washington  and  part  of  eastern  Oregon,  but  buried  the  rest  of 
the  country,  in  part  to  a  great  depth. 

Besides  granite,  the  principal  massive  rock  of  Oregon  and  Washington  is  basalt,  but  andesites  also  occur  in 
great  quantities.  The  bed-rock  of  the  Wickaiser  mine,  Ochoco  district,  Wasco  county,  Oregon,  is  sh«wn  by  a  slide 
in  the  census  collection  to  be  diorite,  proving  at  least  that  earlier  eruptive  rocks  are  not  entirely  absent.  The  ore 
deposits  are  chiefly  veins  in  granite  or  metamorphic  strata,  and  do  not  appear  to  be  associated  with  volcanic  rocks. 

Much  the  most  important  mining  region  of  Oregon  is  Baker  county,  which  lies  in  the  southeastern  corner  of  the 
state  and  adjoins  Idaho.  The  gold  veins  of  this  region  are  in  granite  and  metamorphic  slates  in  and  near  the  Blue 
mountains,  and  may  thus  be  considered  as  occurring  on  a  continuation  of  the  gold  belt  of  California.  They  are 
accompanied  by  auriferous  gravels,  which  are  of  much  local  importance,  though  of  greatly  inferior  volume  to  those 
of  California  and  Idaho.  The  same  arguments  which  are  held  to  prove  the  Tertiary  age  of  the  gravels  of  California 
would  probably  apply  to  these  also,  but  detailed  information  bearing  upon  the  point  is  not  -available.  Trias-Jura 
strata  are  also  exposed  in  the  Cascade  range  at  a  few  points  where  the  overlying  material  has  been  removed  by 
erosion,  and  a  little  gold  quartz  and  gravel  have  been  discovered  in  such  localities ;  for  example,  in  Lewis  county. 

In  the  northern  part  of  California,  as  has  been  mentioned,  the  gold-bearing  rocks  have  a  wide  distribution,  and 
are  not  confined  to  a  comparatively  narrow  belt,  as  they  are  in  the  middle  of  the  state.  Similarly  the  gold  mines  of 
Josephine  and  Jackson  counties,  which  adjoin  California  and  lie  to  the  west  of  the  Cascades,  do  not  seem  to  bear 
a  direct  relation  to  the  main  ranges ;  but  it  is  noteworthy  that  this  region  of  scattered  deposits  in  the  two  states  is 
also  that  in  which  the  Sierra  and  the  Coast  ranges  meet,  and  are  so  entangled  that  as  yet  no  one  has  succeeded  in 
discriminating  the  two  systems.  The  geological  relations  of  the  Skagit  mines,  in  Washington  territory,  on  the 
upper  waters  of  the  Skagit  river,  are  not  known  further  than  that  the  gold  is  found  in  the  bed  of  the  present  streams 
and  that  the  surrounding  country  is  mainly  granitic.  Auriferous  sands  are  found  on  the  southern  coast  of  Oregon, 
as  in  northern  California,  and  are  worked  as  wind  and  tide  permit. 

Coal-beds  are  frequent  in  the  belt  of  country  west  of  the  Cascade  range.  Of  these  the  most  important  are  found 
at  Coos  bay,  in  Oregon,  and  at  Bellingham  bay,  in  Washington  territory.  The  age  of  the  Belliugham  bay  seams  is 
known  to  be  the  same  as  that  of  the  Monte  Diablo  coal  or  Upper  Cretaceous,  and  those  of  Coos  bay  are  probably 
also  of  this  period.  Iron  ore  is  abundant,  aiid  has  been  smelted  to  a  small  extent,  but  under  the  disadvantage  of 
high  rates  for  labor.  Quicksilver  is  found  at  the  New  Idrian  cinnabar  mine,  Douglas  county.  Its  occurrence  seems 
to  be  similar  to  that  of  the  California  mines,  and  it  represents  the  northern  end  of  the  series  of  deposits,  the  southern 
extremity  of  which  is  in  San  Luis  Obispo  county,  California.  It  would  be  incorrect,  however,  to  characterize  this 
entire  series  as  a  "belt",  for  toward  the  north  the  known  occurrences  are  at  long  intervals. 

a  These  are  of  the  Tejon  group,  and  may  prove  to  be  Eocene. 


28 


PRECIOUS  METALS. 


Whatcom  and  Yakima  counties  are  the  only  ones  in  Washington  territory  from  which  gold  mines  are  reported, 
though  small  quantities  of  gold  are  also  obtained  from  the  sands  of  the  Columbia  river,  while  King  and  Thurston 
counties  produce  coal.  Oregon,  Baker,  Grant,  Wasco,  Douglas,  Josephine,  Jackson,  and  TJmatilla  counties  are 
reported  as  containing  gold  mines.  Coos  yields  auriferous  beach  sands  and  coal,  Clackamas  iron,  and  Douglas 

cinnabar. 

OREGON. 

BAKER  COUNTY. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

BURNT  RIVES. 

Granite  

Vein. 
Do. 
Placer. 

Do. 
Do. 
Do. 
Vein. 

Placer. 
Vein. 

Placer. 
Vein. 

Placer. 
Vein. 

CONNER  CREEK. 

Quartz  limonite  (gold  and  Bulphureta)  

Slate,  basalt  dike*  

Slate,  basalt  dike  *  

FARBI8  GULCH. 

Granite  

POCAHONTA8. 

Granite       .           

do                             .           

Salmon  Creek 

do                           

T       P 

Slate 

Slate 

BYE   VALLEY. 

Quartz,  Btromeyerite,  copper  carbonates,  (autimonide 
of  silver  and  ironpyrite). 

SHASTA. 

SILVER  CKEEK. 

Quartz,  mispickel,  pyrite,  (stephanite,  gold  and  silver 
bearing  pyrite). 

(Unknown)  

Granite  

WILLOW  CREEK. 

Slate      

Virtue 

Shale   

Shale 

Examined  microscopically. 
COOS  COUNTY. 


and  gold. 

* 

DOUGLAS  COUNTY. 


Vein. 

GEANT  COUNTY. 


ELK  CREEK. 

Slate  

Placer. 
Do. 

Vein. 
Placer. 
Do. 
Vein. 

Placer. 

Elk  Creek 

do 

GRANITE. 

Buffalo 

Galena,  pyrite,  quartz,  (stephanite  and  mispickel)  
(Auriferous  gravel)  
...  do  .                                   

Slate 

Bame&  Lucas  

Shale 

.  do  

Tctrahedrite.  polybasite,  chalcopyrite,  pyrite,  quartz, 
(mispickel  and  ziucblendo). 

Granite 

Trail  creek     

Granite                     ... 

JACKSON  COUNTY. 


APPLEOATK. 

Chapel  &  Co  

Slate 

Placer. 

Grand  Applegate  

..  do 

do 

Do. 

UNIONTOWN. 

Gin  Lin  

Slate 

Placer. 

KTEIiLING. 

Sterling  

Slate 

Placer. 

GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


29 


JOSEPHINE  COUNTY. 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

GRAVE  CREEK. 

Slate  

• 

Placer. 

TAKE. 

Galena,  pyrite,  chalcopyrite,  and  quarts. 

"WASCO  COUNTY. 


OCHOCO. 

Diorite*                  .... 

Placer. 

*  Examined  microscopically. 

WASHINGTON. 

YAKIMA. 
[None. — Determinations  in  parentheses  are  given  on  the  authority  of  the  expert.] 


FBSHABTOZT. 

Metamorpbio  

Vein. 

BWAKK. 

Swank 

Sandstone  (and  slate)  

Placer. 

GEOLOGICAL  SKETCH  OF  NEVADA. 

That  portion  of  the  wide  area  included  between  the  Sierra  Nevada  and  the  Wahsatch  range,  the  drainage  of 
•which  does  not  find  its  way  to  the  sea,  was  called  the  Great  Basin  by  Fremont.  The  name  has  passed  into  general 
use,  but  with  a  somewhat  extended  signification,  and,  as  commonly  employed,  includes  to  the  south  the  desert 
region  lying  between  the  southern  California  ranges  and  the  Colorado  plateau,  and  to  the  north  so  much  of  Oregon 
as  lies  east  of  the  Blue  Mountain  range  and  a  somewhat  indefinite  portion  of  Idaho.  The  state  of  Nevada,  with 
the  western  half  of  Utah,  constitutes  the  larger  and  more  important  part  of  the  Great  Basin. 

Leaving,  the  mountains  out  of  consideration,  the  basin  may  be  considered  as  a  high  plain  with  an  average 
elevation  of  perhaps  4,500  feet;  but  the  central  portion  is  higher  than  the  edges,  the  belt  of  country  next  west  of 
the  Wahsatch  and  that  next  east  of  the  Sierra  being  about  4,000  feet  above  sea-level,  while  near  the  middle  of 
Nevada  the  elevation  is  about  6,000  feet  above  tide-water. 

The  Great  Basin  is  strikingly  characterized  by  rather  short  mountain  ranges  with  nearly  meridional  trend, 
separated  by  valleys  a  few  miles  wide.  The  culminating  peaks  rise  from  2,000  to  6,000  feet  above  the  level  of  the 
surrounding  country,  and  the  ranges  often  present  an  imposing  appearance,  though  they  are  greatly  inferior  to  the 
Sierra  and  the  Wahsatch  as  topographical  features.  Many  of  the  valleys  are  totally  devoid  of  vegetation,  and 
present  a  surface  of  alkaline  salts  (mostly  sodium  chloride,  carbonate,  or  sulphate),  but  the  greater  portion  of  the 
country  is  thinly  clothed  with  "sage  brush",  low-growing  shrubs  with  dull  gray-green  foliage,  the  most  abundant 
of  which  is  Artemisia  tridentata;  on  the  higher  portion  of  the  mountains,  where  a  certain  amount  of  moisture  is 
supplied  by  the  slow  melting  of  the  scanty  snowfall,  nut-pines,  junipers,  and  mountain  mahogany  grow  to  a  limited 
extent.  The  few  streams  are  also  fringed  with  narrow  belts  of  vegetation. 

The  principal  rivers  of  Nevada  are  the  Humboldt,  the  Carson,  the  Truckee,  and  the  Quinm.  All  of  these  streams 
dwindle  after  reaching  comparatively  level  ground  by  evaporation  and  absorption,  and  at  last  empty  into  small  salt 
lakes  which  have  no  outlets.  The  alkali  deserts  unquestionably  mark  the  positions  of  similar  lakes  now  completely 
dried  away. 

Though  there  are  many  contributions  to  the  geology  of  Nevada,  no  complete  survey  of  it  has  ever  been  made. 
The  exploration  of  the  fortieth  parallel,  however,  covered  a  belt  of  100  miles  in  width  and  extended  across  the- 
statefrom  east  to  west,  beside  taking  in  some  outlying ' districts  of  importance;  and  most  of  the  statements  as  to 
the  general  geology  of  Nevada  in  this  account  are  derived  from  the  publications  of  that  survey. 

The  Archaean  is  exposed  at  a  large  number  of  points  along  the  crests  of  the  mountain  ranges  of  Nevada,  and 
these,  taken  in  connection  with  the  overlying  strata,  show  that  prior  to  the  Palajozoic  era  a  mountain  system  covered 
the  area  of  Nevada  and  extended  to  the  east  as  far  as  the  104th  meridian.  This  system,  however,  seems  to  have 
been  entirely  suboceanic,  for  the  ranges  were  extremely  lofty,  yet  they  presented  broader  and  smoother  surfaces 
than  subaerial  erosion  is  ever  known  to  produce. 

During  the  Palaeozoic  a  continent  occupied  western  Nevada  and  most  of  California,  its  eastern  shore  intersecting 
the  40th  parallel  in  longitude  117°  30'  (a  few  miles  west  of  Austin)  and  trending  nearly  north  and  south.  The 
sediments  from  this  western  continent,  as  well  as  from  comparatively  unimportant  islands,  accumulated  throughout 


30  PRECIOUS  METALS. 

the  Palaeozoic  era  on  the  sea-bottom,  which  subsided  as  the  load  increased,  until  the  strata  reached  the  enormous 
thickness  of  40,000  feet  near  the  shore,  thinning  out  to  the  eastward.  The  Palaeozoic  was  an  era  of  extreme  quiet, 
so  that  the  geologists  of  the  fortieth  parallel  were  able  to  detect  no  unconformity  in  its  strata.  During  the 
Carboniferous  period  the  Paleozoic  sea  was  for  the  most  part  so  deep  that  the  sediments  were  almost  exclusively 
limestones,  in  which  it  is  hopeless  to  look  for  coal.  Near  the  shore,  however,  laud  plants,  associated  with 
carbonaceous  beds,  occur  in"  a  single  horizon,  but  even  this  is  underlaid  and  overlaid  by  calcareous  deposits  and 
is  of  limited  extent.  At  the  close  of  the  Palaeozoic  era  the  land  and  the  sea  changed  places.  The  sea-bottom,  from 
longitude  117°  30'  to  and  including  the  Wahsatch,  rose  above  the  surface  of  the  water,  while  the  continent  which 
had  stretched  to  the  west  sank  and  formed  an  ocean  lloor,  upon  which  the  sediments  from  the  new  continental  area 
were  deposited.  The  Triassic  and  Jurassic  periods  were  also  extremely  quiet,  and  the  strata  are  conformable 
throughout. 

At  the  close  of  tho  Jurassic  age  the  western  ocean,  with  its  original  floor  of  Arcliiean  ranges  overlaid  by  twenty  odd  thousand  feet  of 
conformable  Trias-Jura  sediments,  suffered  abrupt  orographical  uplift,  resulting  in  the  formation  of  a  series  of  sharp  folds  and  elevating 
a  portion  of  the  ocean  area,  extending  from  the  eastern  shore  outward  and  westward  as  far  as  the  present  west  base  of  the  Sierra  Nevada, 
making  an  addition  to  the  continent  of  200  miles,  the  Sierra  itself  constituting  the  most  western  and  most  elevated  of  the  newly-formed 
mountain  ranges.  The  character  of  the  orography  of  this  period  of  disturbance  is  that  of  tangential  compression,  in  which  the  gentler 
action  was  close  to  the  old  shore  in  the  meridian  of  117°  and  most  powerful  in  the  crumpled  western  slope  of  the  Sierra  Nevada,  where  tho 
Triassie  and  Jurassic  series  have  their  enormous  thickness  crushed  into  a  mass  of  almost  indistinguishable  folds,  the  rocks  thrown  into 
vertical  dip  and  crowded  together,  making  a  belt  of  strata  about  lifty  miles  broad.  This  orographical  action  continued  south  ward  as  far 
as  the  denned  range  of  the  Sierra  Nevada  extends  and  northward  along  the  whole  shore  of  the  Pacific,  probably  as  far  as  tho  Alaskan 
peninsula.  Passing  northward  from  the  region  of  the  fortieth  parallel,  where  tho  new  addition  to  tho  continent  measured  about  200 
miles  from  east  to  west,  the  zone  of  crumpled  Mesozoic  was  depressed  so  that  the  new  ocean  shore  at  the  beginning  of  the  Cretaceous  age 
touche'd  the  west  base  of  the  Jurassic  fold  of  the  Blue  mountains  of  eastern  Oregon,  (a) 

It  is  not  certain  that  the  whole  system  of  Basin  ranges  dates  from  the  post-Jurassic  disturbance,  for  the 
corrugation  of  the  Paleozoic  area  east  of  117°  might  have  accompanied  its  uplift  immediately  after  the  Carboniferous. 
There  are  considerable  grounds,  however,  for  supposing  that  uplift  to  have  been  comparatively  quiet,  and  it  is  on 
the  whole  probable  that  all  the  ranges  were  raised  by  the  same  movement  which  crumpled  the  Trias- Jura  strata  of 
the  Sierra. 

The  views  of  the  various  geologists  who  have  studied  the  basin  ranges  are  not  uniform  as  to  the  character  of 
the  dynamical  action  which  resulted  in  the  upheaval  of  these  mountains.  The  geologists  of  the  fortieth  parallel 
regard  the  ranges  as  composed  of  synclinal  and  anticlinal  folds  more  or  less  obscured  by  longitudinal  compression 
and  by  faulting  long  subsequent  to  their  upheaval.  Pfaff  (b)  and  others  hold  that  faults  are  the  extreme  results  of 
forces  tending  to  form  folds  in  an  imperfectly  elastic  material,  and  that  folds  consequently  frequently  pass  over  into 
faults ;  and  as  long  ago  as  1870  Mr.  Ernmons  (c)  pointed  out  a  case  of  this  kind  in  the  Toyabe  range.  Messrs. 
Powell  and  Gilbert,  on  the  other  hand,  from  investigations  made  mainly  to  the  south  of  the  fortieth  parallel  belt, 
maintain  that  many  of  the  uplifts  are  purely  monocliual  in  character. 

The  Cretaceous  is  wholly  wanting  in  the  state  of  Nevada  as  well  as  in  the  great  Sierra.  This  area  was  certainly 
above  sea-level  during  that  epoch,  and  if  any  fresh- water  deposits  formed  they  were  swept  away  before  Tertiary 
strata  covered  and  protected  them.  Professor  Whitney  considers  the  absence  of  Cretaceous  fossils  in  the  Sierra  as 
so  remarkable  that  he  infers  the  possibility  that  this  area  was  unsuited  to  animal  and  vegetable  life,  (d) 

The  Tertiary  and  the  Quaternary  eras  in  Nevada  were  characterized  by  the  presence  of  lakes,  which  occupied 
different  localities  as  orographical  disturbances  altered  the  drainage  system.  The  present  period  of  desiccation, 
during  which  evaporation  has  so  increased  and  precipitation  so  diminished  that  the  lakes  no  longer  overflow  and 
the  salts  brought  into  them  by  the  streams  are  retained  in  nearly  saturated  solution,  has  not  been  a  long  one 
from  a  geological  standpoint;  and,  according  to  Professor  Whitney,  it  is  shorter  than  that  during  which  man  has 
been  an  inhabitant  of  the  Pacific  coast.  Mr.  King  presents  evidence  to  show  that  there  has  been  more  than  one 
period  of  desiccation  in  the  Quaternary. 

The  massive  rocks  of  the  Great  Basin  are  very  numerous,  and  are  referable  to  three  distinct  eras  of  eruptive 
activity.  The  granites  are  found  only  associated  with  A'rcha3an  rocks,  and  never  penetrate  overlying  strata. 
Important  eruptions  of  diorite  and  diabase  accompanied  the  post- Jurassic  upheaval;  while  in  the  Tertiary  and 
Quaternary  andesites,  rhyolites,  and  basalts  were  ejected  in  great  quantities,  usually  reaching  the  surface  along  lines 
of  disturbance  established  in  the  Mesozoic  era.  The  crests  of  a  large  portion  of  the  Nevada  ranges  are  still  covered 
by  these  lavas,  among  which  rhyolite  predominates.  Propylite,  which  had  been  supposed  to  exist  at  a  number  of 
points  in  the  Great  Basin,  does  not  appear  to  be  an  independent  rock,  but  to  represent  a  certain  stage  of 
decomposition,  (e) 

Eeceut  advances  in  the  microscopical  study  of  rocks  tend  to  show  that  sanidiu  feldspar  is  of  much  rare 
occurrence  than  has  hitherto  been  supposed.  A  recent  revision  (/)  of  the  fortieth  parallel  collection  by  Messrs. 

a  Exploration  of  the  Fortieth  Parallel,  vol.  i,  p.  537.  d  Auriferous  Gravels,  p.  319. 

6  Mechanimius  der  Gebirgsbilding.  e  Monographs  United  States  Geological  Survey,  vol.  iii. 

c  Exploration  of  the  Fortieth  Parallel,  vol.  iii,  326.  /  Third  Animal  Report  of  the  United  States  Geological  Survey. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  31 

Hague  and  Iddiugs,  to  the  results  of  which  the  writer  has  had  access  in  advance  of  their  publication,  shows  that 
there  are  probably  no  true  trachytes  among  the  rocks  hitherto  collected  from  the  Great  Basin. 

Ore  deposits  occur  at  a  great  number  of  points  in  Nevada,  carrying  gold,  silver,  lead,  copper,  and  other  useful 
minerals.  They  are  not  limited  to  rocks  of  any  age.  The  Archaean  granite  of  Austin,  the  Palaeozoic  strata  of  Eureka 
and  White  Pine,  and  the  Mesozoic  rocks  of  Washoe  are  sufficient  examples  of  this  fact.  The  deposits  oceur  in  the 
mountains,  as  is  usual  the  world  over,  and  as  the  Nevada  mountains  are  disposed  in  parallel  ranges,  of  course  the 
mines  also  occur  in  parallel  belts.  There  is  a  perceptible  tendency  to  the  development  of  the  same  minerals  at 
different  points  on,  the  same  belt,  though  there  are  no  ore-bearing  zones  comparable  in  continuity  with  the  gold  and 
the  quicksilver  belts  of  California.  The  possibility  that  the  deposits  of  Battle  mountain,  Austin,  Oaudalaria,  etc., 
form  a  continuation  of  the  Arizona  belt  has  already  been  adverted"  to.  . 

In  most  cases  it  is  impossible  to  determine  the  age  of  the  deposits,  yet  there  are  many  phenomena  indicating  a 
connection  between  them  and  eruptive  activity,  and  they  are  probably  for  the  most  part  referable  either  to  the  post- 
Jurassic  period  of  upheaval  or  to  that  of  the  more  recent  volcanic  eruptions.  The  gold  veins  of  California,  as  has 
been  explained,  are  post- Jurassic;  and  the  Idaho  gold  veins  are  probably,  at  least  in  part,  of  the  same  age.  It  is 
difficult  to  suppose  that  the  similar  physical  conditions  prevailing  in  Nevada  during  the  same  period  were  not 
attended  by  similar  mineralogical  results.  The  Comstock,  however,  is  probably  very  recent  and  a  concomitant  of 
volcanic  eruptions  in  its  immediate  neighborhood.  Mr.  King  drew  attention  (a)  to  the  fact  that  no  ore  pebbles  have 
been  found  in  the  Tertiary  lake  beds  of  Nevada,  and  this  statement  still  remains  valid  so  far  as  the  exploration  of 
the  fortieth  parallel  is  concerned.  Nor  are  prospectors  known  to  have  found  any  indications  of  ore  in  these  beds. 
This  negative  evidence  is  all  in  favor  of  the  supposition  that  the  deposits  are  mainly  Tertiary  and  post-Tertiary. 

THE  COMSTOCK  LODE. — The  Comstock  lode  is  situated  in  Storey  county,  about  10  miles  from  the  eastern  limit 
of  the  Sierra,  and  lies  on  the  east  flank  of  the  Virginia  range.  In  twenty-one  years  it  has  produced  a  little  over 
$306,000,000  worth  of  bullion,  of  which  $132,000,000  was  gold.  The  mines  on  this  lode  are  the  deepest  in  America, 
reaching  a  distance  of  over  3,000  feet  from  the  surface,  and  containing  185  miles  of  galleries.  The  lode  is  extremely 
wide  in  places,  and  has  been  traced  horizontally  for  about  4  miles.  It  dips  east  at  an  angle  of  about  45°. 

The  Washoe  district  is  almost  entirely  made  up  of  eruptive  rocks  of  post-Jurassic  and  Tertiary  age.  These 
are  in  large  part  highly  decomposed,  and  both  their  character  and  the  structural  relations  of  the  vein  have  given 
rise  to  much  difference  of  opinion  between  observers.  According  to  the  latest  investigation,  (b)  the  most  productive 
portion  of  the  lode  is  associated  with  a  hanging  wall  of  diabase,  while  the  foot  wall  in  Virginia  City  is  diorite,  and 
in  Gold  Hill  metamorphic  slate.  To  the  north  and  south  of  the  most  productive  portion  of  the  lode,  which  has 
hitherto  been  between  the  Union  aud  Overman  mines,  the  vein  ramifies,  only  its  northeastern  branch  remaining  in 
contact  with  the  diabase. 

A  great  fault  attended  the  opening  and  filling  of  the  vein.  Its  throw  was  nearly  3,000  feet  at  the  middle  of 
the  lode,  diminishing  in  each  direction  toward  the  extremities.  The  faulting  action  resulted  in  the  formation  of  a 
system  of  fissures,  which  divides  the  country  rock  on  each  side  into  a  series  of  parallel  sheets.  By  this  means  tho 
east  wall,  which  was  depressed  by  the  fault,  assumed  near  the  surface  the  shape  of  a  sharp  wedge,  and  the 
projecting  edge  was  broken  through,  giving  rise  to  a  secondary  fissure,  forming  an  angle  of  30°  to  45°  with  the  lode 
plaue.  The  lode  was  charged  with  ore  and  quartz  by  lateral  infiltration  from  the  east  or  hanging  side,  these 
materials  being  deposited  wherever  there  was  an  open  space  or  a  space  filled  with  loose  fragments  to  receive  them. 
Of  such  spaces  the  secondary  fissure,  or  "east  vein",  as  it  has  been  called,  afforded  a  large  number,  while  below 
the  junction  of  this  fissure  with  the  main  lode  such  openings  were  comparatively  infrequent.  The  fault  mentioned 
did  not  take  place  all  at  once,  and  probaWy  consisted  of  a  great  number  of  small  movements,  all  in  the  same 
direction,  extending  over  the  whole  period  of  ore  deposition.  Although  small,  these  movements  took  place  with 
irresistible  force,  and  crushed  such  ore  bodies  as  crossed  the  lines  of  motion  to  such  an  extent  that  their  substance 
resembles  ordinary  commercial  salt  in  texture  and  appearance. 

As  is  usually  the  case  in  silver  veins,  the  distribution  of  ore  in  the  quartz  was  by  no  means  regular;  a  fact 
probably  depending  on  the  irregularity  of  the  leachiug  process.  While  very  little  of  the  quartz  is  free  from  traces 
of  precious  metals,  only  certain  spots  contain  enough  to  pay  the  expense  of  extraction,  and  are  hence  known  as 
"  bonanzas  ".  (c)  These,  however,  commonly  occur  in  the  largest  quartz  masses. 

Though  the  Comstock  is  not  just  now  in  a  flourishing  condition,  there  seems  to  be  no  reason  why  large  ore 
bodies  should  not  yet  be  met  with.  The  first  condition  for  an  ore  body  is  a  space  to  receive  it.  The  existence  of 
such  openings  depends  upon  mechanical  conditions  which  are  likely  to  be  repeated  at  almost  any  depth,  though 
a  series  of  bonanzas  on  one  level,  such  as  was  found  in  the  "  east  vein  ",  is  not  likely  to  recur. 

It  is  highly  probable  that  the  depth  to  which  the  Comstock  can  be  explored  will  be  limited  by  the  extraordinary 
heat.  The  Gold  Hill  mines  have  been  flooded  with  water  of  a  temperature  of  170°  F.,  and  as  the  temperature  of 
the  rock  and  the  water  increases  on  the  whole  in  direct  proportion  to  the  depth  boiling  water  may  be  met  at 

a  Exploration  of  the  Fortieth  Parallel,  vol.  iii,  p.  7. 

6  Monographs  United  States  Geological  Survey,  vol.  iii. 

c  A  Spanish  term,  the  nearest  equivalent  of  which  is  "pay  rock". 


32  PRECIOUS  METALS. 

almost  any  time  after  the  4,000-foot  level  is  reached.    The  heat  of  the  water  and  the  rock  is  a  remnant  of  volcanic 
action. 

AUSTIN. — The  property  of  the  Manhattan  Mining  and  Milling  Company  is  situated  at  Austin,  Lander  county,  (a) 
It  is  famous  for  its  steady  yield  of  above  $1,000,000  of  silver  a  year  from  very  rich  but  also  very  rebellious  ores. 
The  Toyabe  range,  on  which  Austin  lies,  is  near  the  western  edge  of  the  Palaeozoic  area  which  occupies  the  eastern 
half  of  the  Great  Basin.  It  has  a  granitic  axis  flanked  by  Paleozoic  strata,  and  is  capped  to  a  considerable  extent 
by  rhyolite.  Other  eruptive  rocks  occur  in  the  range,  which  must  be  for  the  present  regarded  as  of  uncertain 
character.  The  most  important  mineral  deposits  are  found  as  veins  in  the  granite,  chiefly  on  the^outheru  slope  of 
Lander  hill. 

The  outcrops  on  the  hillside  are  very  numerous,  and  many  locations  have  been  made ;  some  within  10  or  20  feet  of  each  other.  Some 
of  these  outcrops  have  been  proved  by  actual  development  to  be  well-defined  and  persistent  fissures:  others  are  probably  mere  seams  or 
branches  that  pinch  out  or  unite  with  stronger  veins  in  depth ;  and  that  many  must  disappear  in  this  manner  seems  apparent,  from  the 
fact  that  the  number  of  veins  or  fissures  cut  in  the  deeper  cross-cuts  and  shafts  in  various  parts  of  the  hill  boar  a  very  small  proportion 
to  the  number  of  outcrops  at  the  surface  in  their  immediate  vicinity,  which,  if  persistent,  would  appear  below. 

The  developments  on  Lander  hill  show  that  within  this  mineral  belt,  running  north  and  south,  there  prevails  a  zone  more  favored 
than  the  rest,  within  the  limits  of  which  the  northwest  and  southeast  veins  traversing  it  are  especially  rich  iu  ores  of  high  value,  and 
beyond  which  the  proportion  of  base  metals  is  greatly  increased.  This  zone,  so  far  as  understood,  also  has  a  north  and  south  direction. 
On  Lander  hill  it  may  be  from  a  quarter  to  a  half  mile  in  width.  Its  western  limit  is  thought  to  pass  through  the  Diana  and  the  Savage 
mines,  so  that  in  passing  from  the  southeastern  to  the  northwestern  portions  of  those  claims  a  perceptible  diminution  of  the  richer  aud 
purer  silver-hearing  minerals,  and  an  increasing  predominance  of  baser  metals,  such  as  load,  copper,  zinc,  antimony,  and  iron,  take  place. 
Proceeding  still  further  west,  the  proportion  of  rich  silver  minerals  to  the  baser  compounds  becomes  still  less,  until  the  ore  is  quite  too 
poor  to  pay  for  extraction,  (ft) 

The  veins  are  comparatively  very  narrow,  none,  so  far  as  reported,  exceeding  3  feet.  Many  of  them,  however, 
are  so  rich  that  they  can  be  worked  with  profit  when  showing  only  3  inches  of  ore.  The  ore  minerals  are  pyrargyrite, 
proustite,  stephanite,  polybasite,  tetrahedrite,  argentiferous  galena,  zincblende,  and  iron  and  copper  pyrites.  The 
amount  of  gold  is  said  to  be  so  small  as  not  to  pay  for  separation.  The  gangue  minerals  are  chiefly  quartz, 
manganese-spar,  and  calcite.  Near  the  surface  the  veins  carried  the  silver  as  chloride,  but  at  a  depth  of  150  feet 
this  facile  ore  was  replaced  by  the  rebellious  compounds  above  mentioned.  There  can  be  little  doubt  that  the 
chloride  was  formed  by  the  decomposition  of  the  more  complex  minerals. 

The  granite  at  a  distance  from  the  veins  is  extremely  hard  and  tough,  but  near  the  ore  it  is  much  softer  and 
shows  signs  of  decomposition.  A  slide  of  this  rock  in  the  census  collection  shows  that  it  is  a  normal  biotite 
granite  which  has  been  subjected  to  the  action  commonly  known  as  solfataric.  The  mica  has  been  in  part  converted 
into  chlorite,  and  in  this  latter  mineral  bunches  of  epidote  crystals  have  developed,  evidently  at  the  expense  of 
the  chlorite,  while  the  feldspar  is  scarcely  affected.  This  fact,  taken  in  connection  with  the  relations  of  the  altered 
rocks  and  the  whole  character  of  the  occurrence,  leads  to  the  supposition  that  the  veins  were  deposited  by  lateral 
secretion.  All  the  veins  are  faulted  to  the  north  for  a  distance  of  about  200  feet,  and  Mr.  Emmons  considers  it  not 
improbable  that  this  dislocation  accompanied  the  eruption  of  the  rhyolite  which  forms  mount  Prometheus. 

The  age  of  formation  of  the  veins  is  uncertain.  The  fact  that  faults  have  taken  place  since  the  ore  was  deposited 
is  at  least  compatible  with  the  supposition  that  the  deposits  are  post- Jurassic ;  but  were  this  the  case,  eruptive 
rocks  of  the  same  age  would  probably  be  formed  in  the  neighborhood,  while  none  such  have  been  recognized.  The 
formation  of  the  veins  is  naturally  connected  with  the  raetaphorism  of  the  sedimentary  rocks  of  the  range,  which 
seems  to  be  due  to  later  volcanic  eruptions.  The  fact  that  the  number  of  croppings  occurring  at  the  surface  was 
larger  than  that  of  the  veins  found  at  a  comparatively  slight  depth  jvould  also  lead  one  to  suppose  that  this 
multiplicity  of  outcrops  was  a  surface  phenomenon,  and  that  no  great  erosion  had  taken  place  since  the  ore  was 
deposited.  It  is  not  impossible  that  the  lines  of  fracture  were  established  iu  post- Jurassic  times,  and  that  the  tilling 
of  the  veins  and  their  dislocation  occurred  much  later. 

The  mines  of  the  Manhattan  Company  cover  a  large  extent  of  ground,  more  than  a  square  mile,  but  the  greatest 
depth  reached  is  only  900  feet.  The  small  size  of  the  veins  makes  mining  extremely  expensive  however,  a  very 
large  amount  of  waste  being  necessarily  extracted  in  sloping  the  veins.  The  richness  of  the  ore  is  indicated  by  the 
fact  that  it  is  mixed  for  roasting  so  as  to  give  a  tenor  of  $250.  The  milling' process  consists  in  crushing  dry, 
roasting  with  salt  in  a  Stetefeldt  furnace,  and  amalgamation  in  pans. 

EUREKA  DISTRICT. — The  value  of  the  ore  deposits  of  Eureka  was  not  determined  until  the  year  1870,  since 
which  time,  however,  this  has  been  one  of  the  most  important  lead-  and  silver-producing  districts  of  the  country. 
It  now  produces  about  $4,600,000  of  gold  and  silver,  aud  nearly  or  quite  12,000  tons  of  lead  annually. 

It  is  remarkable  geologically  as  affording  a  very  extensive  section  of  Palaeozoic  strata.  It  has  recently  formed 
the  subject  of  a  detailed  investigation  by  Mr.  Arnold  Hague,  whose  monograph  on  the  Geology  of  the  Eureka 
District  will  appear  about  the  same  time  as  this  volume.  He  has  kindly  given  permission  to  print  the  accompanying 
section,  showing  the  average  thickness  and  the  succession  of  the  rocks,  and  indicating  by  a  double  line  a  non- 
conformity in  the  Silurian,  the  first  thus  far  discovered  in  the  Palaeozoic  of  the  Great  Basin. 


a  Mr.  8.  F.  £muious  has  reported  on  the  geology  of  the  Toyabe  range,  and  Mr.  J.  D.  Hague  on  the  mining  and  milling  at  Reese  river. 
Exploration  of  the  Fortieth  Parallel,  vol.  iii. 

6  Exploration  of  the  Fortieth  Parallel,  vol.  iii,  p.  351. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


33 


GEOLOGICAL  SECTION  OF  THE  EUREKA  DISTRICT. 
BY  MB.  AUXOLD  HAGUE. 


4 

500 

Light-colored  blue  and  drab  limestones.                                • 

i 

2,000 

Coarse  and  fine  conglomerates,  with  angular  fragments  of  chert  ;  layers  of  reddish-yellow  sandstone. 

ct" 

0 

3,800 

Heavy  bedded  dark-blue  and  gray  limestone,  with  intercalated  bands  of  chert  ;  argillaceous  beds  near  the 

base. 

c 

3 

3  000 

O 

i 

White-pine  shale  

2,000 

Black  argillaceous  shales,  more  or  less  arenaceous,  with  intercalations  of  red  and  reddish-brown  friable 

o 
o 
o 

sandstone,  changing  rapidly  with  the  locality.    Plant  impressions. 

J" 

6  000 

Lower  horizons  indistinctly  bedded,  sacuharoidal  texture,  gray  color,  passin^up  into  strata,  distinctly  bedded, 

i 

brown,  reddish-brown,  and  gray  in  color,  frequently  finely  striped,  producing  a  variegated  appearance. 

The  upper  horizons  are  massive,  well  bedded,  aud  bluish-black  in  color.    Highly  fossiliferons. 

. 

1  800 

1 

Trenton  fossils  at  the  base.    Ualloysites  in  the  upper  portion. 

to" 

500 

R 

2  700 

Interstratified  limestone  argillites  and  arenaceous  beds  at  the  base,  passing  into  purer,  fine-grained  limestone 

a 

CO 

of  a  bluish-gray  color,  distinctly  bedded.     Highly  fossiliferous. 

350 

Yellow  argillaceous  shale  layers  of  chert  nodules  throughout  the  bed,  but  more  abundant  near  the  top. 

. 

1 

1  200 

Dark-gray  and  granular  limestone.    Surface  weathering  rough  and  ragged  ;  only  slight  traces  of  bedding. 

n 

I 

Secret  Canon  shale  (overlies  the  ore- 
bearing  rock). 

1,600 

Yellow  and  gray  argillaceous  shales,  passing  into  shaly  limestone.    Near  the  top  interstratiHed  layers  of 
shale  and  thinly-bedded  limestone. 

1 

Prospect  Mountain  limestone  (incloses 
the  ore  deposits*. 

3,050 

Gray  compact  limestone,  lighter  in  color  than  the  Hamburg  limestone,  traversed  with  thin  seams  of  cnleite. 
Bedding-planes  very  imperfect. 

Prospect  Mountain  qnartzite  (under- 
lies the  ore-bearing  rock). 

1,500 

Bedded  brownish-white  quartzites,  weathering  dark-brown  ;  ferruginous  near  the  base.    Intercalated  thin 
layers  of  arenaceous  shales.    Beds  whiter  near  the  summit. 

It  appears  from  this  table  that  the  ore  deposits  lie  in  the  lower  horizons  of  the  Cambrian.  When  they  were 
formed  is  quite  another  question.  The  district  shows  a  number  of  massive  rocks,  viz:  Archaean  granite  and 
Tertiary  or  post-Tertiary  andesites,  dacite,  rhyolite,  and  basalt.  The  eruptions  most  closely  associated  with  the 
mines  were  rhyolite,  and  a  connection  between  this  rock  and  the  ore  may  fairly  be  suspected ;  but  the  deposits  are 
still  under  investigation,  and  something  more  satisfactory  regarding  their  nature  and  genesis  than  any  speculation 
which  could  be  offered  hece  will  probably  soon  be  ready  for  publication. 

The  ores  of  Kuby  Hill  are  argentiferous  galena,  accompanied  by  its  decomposition  products.  Indeed,  the  larger 
part  of  the  ore  thus  far  mined  is  carbonate,  mixed  with  some  sulphate  aud  ocher,  as  well  as  with  mimetite  and 
wulfenite,  the  occurrence  of  which  indicates  the  presence  of  considerable  quantities  of  other  metalliferous  mineral 
besides  galena  prior  to  decomposition.  The  ore  bodies  are  irregular,  kidney-shaped  masses  distributed  in  limestone. 
This  rtfck,  though  highly  metamorphosed,  is  distinctly  stratified  in  parts,  and  has  been  proved  by  Mr.  Hague's  party 
to  carry  fossils  which  determine  its  age  as  Cambrian.  The  nature  of  these  ore  deposits  has  formed  the  subject  of 
repeated  lawsuits,  and  the  many  well-known  geologists  and  mining  engineers  who  have  given  testimony  on  the 
subject  have  expressed  very  discordant  views,  some  holding  them  to  be  pipe  veins  in  the  limestone,  while  others 
regard  the  whole  limestone  formation  between  the  quartzite  and  the  shale  as  ore-bearing,  the  barren  portions 
answering  to  the  bone  in  coal  seams.  While  the  one  party  consider  the  small  seams  of  ore  sometimes  found 
connecting  the  ore  bodies  as  the  rake  vein  corresponding  to  the  pipes,  the  other  party  attributes  these  seams  to 
the  accidental  presence  of  fissures,  and  ascribes  no  significance  to  them.  The  diversity  of  opinion  developed  as 
regards  the  deposits  of  Kuby  Hill  appears  to  indicate  merely  that  large  financial  interests  are  involved  in  rlie  title 
to  this  property,  and  not  that  there  is  anything  exceptional  in  the  character  of  the  deposits  themselves.  Lead  on-s 
are  more  often  found  in  limestone  than  elsewhere,  aud  when  so  found  almost  always  exhibit  great  irregularity  in 
form  and  distribution.  The  fact  is  that  little  is  definitely  known  with  reference  to  the  ino/his  opemndi  of  tin- 
deposition  of  galena.  As  Mr.  Ernmons,  (a)  in  discussing  the  deposits  of  Leadville,  has  pointed  out,  if  the  hypothesis 


VOL- 


a  Second  Annual  Report  of  Director  of  United  States  Geological  Hiirn-y. 


34  PliECIOUS  METALS. 

often  advanced  that  -this  ore  has  been  deposited  in  pre-existing  caves  were  correct  concentric  structure  would 
necessarily  result.  He  regards  it  as  more  probable  that  the  ore  has  been  deposited  by  substitution  for  limestone. 
If  this  can  be  shown  conclusively,  lead  deposits  of  this  character  would  have  to  be  regarded  as  veins  differing 
from  the  usual  typo  merely  iu  the.extreme  irregularity  of  the  walls;  for  an  ordinary  vein  is  merely  an  opening  in 
the  rocks,  which  is  always  limited  iu  horizontal  extent,  and  probably  also  iu  depth.  Into  such  a  fissure  metalliferous 
solutions  percolate  and  deposit  ore  minerals,  precipitation  being  due  to  chemical  or  physical  causes.  Usually 
the  walls  of  veins  are  chemically  inert,  and  hence  do  not  lose  their  original  form  ;  but  if  the  substance  of  the  walls 
of  a  vein,  instead  of,  e.  0.,  infiltrations  of  organic  matter,  were  to  induce  precipitation,  that  fact  certainly  would  net 
deprive  the  resulting  deposit  of  its  character  as  a  vein,  though  the  shape  of  the  walls  might  be  strangely  modified. 
A  very  remarkable  feature  of  the  Eureka  deposits,  shared  to  a  greater  or  less  degree  by  many  others  iu  the 
Great  Basin,  is  the  great  depth  to  which  decomposition,  involving  an  accession  of  oxygen,  has  proceeded.  The 
mines  are  between  1,200  and  1,300  feet  deep ;  yet,  although  some  water  has  been  met  of  late,  the  permanent  water- 
level  has  not  been  reached,  and  the  amount  of  galena  in  the  ore  is  scarcely  more  than  enough  to  prove  that  the 
original  lead  mineral  was  the  sulphide.  The  conversion  of  the  galena  to  carbonate  and  sulphate,  which  must 
clearly  be  ascribed  to  the  agency  of  atmospheric  oxygen,  could  take  place  to  such  a  depth  only  in  an  extremely  dry 
country  such  as  the  Great  Basin  now  is,  and  the  decomposition  must  therefore  have  been  accomplished  since  the 
early  Quaternary. 

CHURCHILL  COUNTY. 

The  product  of  this  county  has  for  the  most  part  been  confined  to  borax,  but  there  are  quartz  veins  in  the  IXL 
district  occurring  in  granite  and  on  the  contact  between  granite  and  limestone.  They  carry  silver  and  galena,  but 
were  not  worked  during  the  census  year. 

ELKO  COUNTY. 

The  deposits  of  the  Tuscarora  district,  in  this  county,  are  silver  ores,  including  light  and  dark  ruby  silver, 
stephauite,  argentite,  and,  near  the  surface,  horn-silver.  They  are  accompanied  by  pyrite.  often  argentiferous,  and 
form  veins  in  highly  decomposed  eruptive  rock.  This  was  formerly  considered  to  be  propylite,  but  from  the  slides 
and  specimens  of  the  census  collection  and  of  the  fortieth  parallel  collection,  and  from  known  occurrences  in  the 
neighborhood,  it  is  probable  that  the  rock  should  be  regarded  as  an  altered  hornblende  andesite. 

ELKO. 

[NoTK. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


• 

WAI 

JA 

Character  of 

Foot 

Hanging. 

deposit. 

WJSCABOBA. 

Belle  Isle 

Vein 

do 

do 

Do 

Grand  Prize  

stcphauite  ;  gangue  country  rock. 
Light  and  dark  ruby  silver,  argentite,  hom-silver  near 

do  

Do. 

surface  ;   gangue  quartz,  iron  and  copper  pyrite, 
anil  ziucblende. 

do 

do 

Do 

Navajo  

Chloride  ;  gangue,  (quartz  and  spar)  

Andesite* 

Do 

North  Belle  Isle  

(Chloride,  ruby,  and  argentiferous  pvrite;   gangue, 

Do. 

Silver  Star  

spar,  and  quartz.) 

Do 

spar,  and  quartz.) 

*  Microscopically  examined. 


ESMERALDA  COUNTY. 

Most  of  the  mines  of  this  county  exploit  deposits  iu  the  metainorphie  slates  and  schists.  These  are  broken 
through  at  numerous  points  by  volcanic  rocks,  especially  basalt,  to  which  the  solfataric  action  attending  the 
formation  of  the  ores  is  possibly  due.  The  ores  resemble  some  of  those  found  in  Inyo  county,  California,  carrying 
sulphautirnonides  of  silver,  argentiferous  galena,  tetrahedrite,  copper  and  iron  pyrite,  zincblende,  and  pyrolusite,  in 
a  quartz  gangue.  There  are  also  gold-quartz  veins  in  granite,  similar  to  those  of  California.  In  the  Columbus 
district  there  is  a  nickel  vein. 

The  Northern  Belle  mine  is  sunk  on  a  series  of  irregular  deposits,  forming  a  belt  which  is,  in  general,  conformable 
to  the  slates  in  which  it  lies.  There  is  much  basalt  in  the  immediate  neighborhood.  Most  of  the  ore  is  oxidized, 
but  a  few  bunches  of  sulpburets  are  left,  carrying  galena,  tetrahedrite,  etc.  The  Northern  Belle  produces  about  a 
million  a  year. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


ESMEKALDA. 
[NOTE.— Determinations  in  parentheses  »re  given  ou  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

CULUHBUI. 

Mount  Potosi      

Gold  and  calcareous  ocher,  (lead,  said  to  carry  silver 
and  gold);  ganguo  quartz;  (autimonial  compounds). 

Nickel  in  an  indeterminable  form. 
(Same  as  Northern  Belle.) 

Horn-silver,   malachite,    galena,    and    tetrahedrite  ; 
gangne,    iron    oxide,    pyrolusite,    pyrite,    quartz, 
(ziucblende). 

(Horn-silver,  malachite,  galena,  and   antimoiiial  sil- 
ver) ;  gangup  quartz,  and  iron  oxide. 

Slate  

Veto. 

Do. 
Do. 

Vein. 
Vein. 

Mineral  belt. 
Do. 

Nickel                      

Slate  (called  porphyry)  

Slate 

Monte  Diablo    

Northern  Belle     

Victor                       

(Slate) 

E.SSIEKALOA. 

ONEOTA. 
Indian  Queen  

Galena  and  chalcopyrite,  (small  quantities  of  snlph- 
antimonidcs  of  silver);  gangue,  pyiite,  quartz,  and 
eincblende. 

(Gold);  gangne  quartz,  iron  and  copper  pyrites  

Mica-schist  

Mica-schist 

WIL8OH. 
Wilson  

Granite  

Rhyolite  and  limestone  
do 

Wheeler  

do  

....do  

EUREKA  COUNTY. 

The  chief  deposits  of  this  county,  those  of  Ruby  Hill,  have  been  sufficiently  enlarged  upon.  Most  of  the  others 
are  also  of  lead  ores,  and  occur  either  in  or  close  to  limestone,  but  some  of  them,  those  for  instance  of  Cortez  district, 
are  accompanied  by  copper  minerals,  native  silver  and  mispickel,  and  some  have  more  or  less  quartz  as  gangue. 
These  are  of  especial  value  in  smelting  the  prevailing  extremely  basic  ores. 

EUREKA. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


WA] 

U* 

Character  of 

Foot. 

Hanging. 

deposit 

COKTM. 

Chloride    galena,    tetrrfhedrite,    native    silver,  and 

EUREKA. 

Alexandria  

malachite  ;    gangue,    zinc  blonde,    and     mispickel, 
(quartz). 

Cernssite  (gold  and  silver,  gangue  quartz  and  iron 

Eldorado  No.  2  

oxide.) 
(Carbonate  silver  and  gold,  gangne  quartz  and  iron 

Eureka  Consolidated  •> 

oxide.) 

do 

do 

wulfenite,  with  limonite  and  aragonite  gangue. 

pipe  veins. 

Phcenix              J 

....do..  

...  do  

and  iron  oxide.) 

Shale. 

SECRET  CASON. 

Irregular  maas. 

EUIIEKA. 

oxide. 

Limestone. 

HUMBOLDT  COUNTY. 

Most  of  the  veins  are  in  the  Mesozoic  slates,  and  carry  ruby  silver  and  stephanite  with  iron  and  copper  pyrite 
and  mispickel  in  a  quartz  gangue.  Near  the  croppings  the  silver  takes  the  form  of  chloride.  Some  of  the  veins  in 
the  slates  are  worked  for  gold,  but  of  these  a  part  will  probably  be  found  to  carry  more  silver  than  gold  when  the 
water-level  is  passed.  The  Pride  of  the  Mountain,  Winnemucca  district,  is  reported  to  be  on  a  contact  between 
slate  and  granite. 


PRECIOUS  METALS. 


HUMBOLDT. 
— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangno. 

WALLS. 

Character  of 
deposit. 

Foot 

Hanging. 

MOUNT  ROSE,  OB  PAKADI6E. 

Big  Nick 

Slate  

Slate 

Vein. 
Do. 

Do. 
Do. 

Vein. 
Contact  vein. 

Bullion  of  Paradise        

Chloride,  pyargyrite,  (rn  by  and  stephanite)  ;  pangue 
quartz,  p'yrite,  mispickel,  chalcopyrite,  and  iron 
oxide. 

do  

..  do  . 

do.    . 

do 

do  

....do  

..    do 

SIERRA,  OB  DUN  GLEN. 

Silicifiod  sedimentary  rock 
(called  porphyry). 

(Slate)  

Silicifled  sedimentary  rock 
(called  porphyry). 

(Slate) 

WINXEMUCCA. 

(Snlphurets  and  antimonial  silver  minerals,  with 
quartz  gangue.) 

(Slate)  

(Granite) 

LANDEK  COUNTY. 

Besides  the  Austin  mines,  sufficiently  described  above,  there  are  veins  of  ruby  silver,  etc.,  in  quartzite,  and  of 
galena  with  quartz  gangue  in  Palaeozoic  slate. 

LANDEK. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

BATTLE  MOUNTAIN. 

Slate  

Vein. 
Vein. 
Vein. 

LEWIS. 

KEEBE  EIVKR. 

Dark  and  light  ruby  silver,  stepbanito,  polybasite, 
tetrahedrite,  galena,  iron  and  copper  pyrites,  and 
quartz. 

Granite* 

*  Microscopically  examined. 


LINCOLN  COUNTY. 

This  county  shows  several  classes  of  deposits.  There  is  a  considerable  number  of  occurrences  of  galena  and 
its  decomposition  products  in  limestone  similar  to  those  of  Eureka,  uud  elsewhere,  and  which  seem  especially 
abundant  in  the  Palaeozoic  limestone  of  the  Great  Basin.  The  Meadow  Valley  and  .Raymond  &  Ely  are  also  in 
metamorphic  strata;  but  these  are  quartzites,  not  limestones,  and  the  character  of  the  ore  is  correspondingly  different. 
Below  the  water-level  the  ore  consists  of  sulphurcis  of  unspecified  composition;  above  the  water-level  it  carries 
horn-silver,  some  gold,  a  little  lead,  and  manganese.  In  the  Eldorado  district  there  are  mines  in  a  massive  rock, 
probably  diorite,  which  carry  argentiferous  copper  minerals. 

LINCOLN. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 

deposit. 

Foot.                                         Hanging. 

BRISTOL. 

Hillside  

Limestone. 

Granite. 
Li  m  oat  one. 

I'robuHy  dioritf. 
Granite  *  :  

Limestone  

Vein. 
Pockets. 

Vein. 
Do. 

Quartz-porphyry  and  shale.  . 

Mendha  

El.DOBADO. 

Januarv  ....          

(Horn-nil  vcr),  iron  oxide  .•  
Srromeyt'i  it  i1,  quart/,  ami  f-alcitc  

Argentiferous  ^al^na  aud  lead  carbonate,  red  copper 
oro  HIM!  malachite,  manganese  o\'Kio,  (cale-spar  aud 
iron  oxide). 

(Gold.  horn-allver,  quartz,  iron  oxide,  and  manganese 
oxide.) 

....do  

Probably  d  iorite  
Granite*.   

LiUH'HtolU!   

Savage 

JACK  BABBIT. 

Dav  

ELY. 

Meadow  Valley  - 

Raymond  Si  Ely  

do 

do 

Brooklyn  

Galena,  ziucblemle,  iron  pyrites,  (antimouial  silver 
aud  quartz). 

Silicrous  limestone. 

MiiTosconii  ally  examined. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


37 


NYE  COUNTY. 

Argentiferous  lead  ores,  inclosed  in  limestone  in  the  usual  irregular  masses,  veins  of  silver  and  copper  ores, 
accompanied  by  slate  or  granite  as  well  as  limestone  as  wall  rocks,  and  veins  of  arsenical  and  antimouial  silver 
ores,  inclosed  in  quartz-porphyry,  are  all  found  in  Kye.  The  famous  Belmont  mine  is  on  a  vein  in  Silurian  slate 
which  lies  between  granite  and  limestone.  The  vein  is  conformable  with  the  slate,  and  carries  sulpho-salts  of  copper, 
silver,  and  lead. 

NYE. 
(NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  and  gaogne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

BELMOXT. 

Galena,  probably  stephnnite,  qnartz,  pyrite,  (sulphur- 
eta  of  lead,  copper,  and  silver). 

Sulpbnrets,  arsenical  and  antimouial  silver  minerals 
and  mispickel. 

Knby  silver  anil  sulphnrets,  arsenical  and  antimonial 
silver  minerals,  aud  manganese  spar, 
do        

Slate  between  granite  and 
limestone. 

Quartz-porphyry  *  

Slate  

Vein. 

Vein. 
Do. 
Do. 

Contact  vela. 
Mineral  belt. 

MORKY. 

Quartz-porphyry  *  

do 

do    

...do  

...  do  

TIBO. 
Tybo  Consolidated  

Galena  and  decomposition  products,  (horn-silver,  iron 
oxide,  quartz,  aud  argentite). 

Galena,  horn-silver,  (copper  ores,  native  silver,  lime- 
stoiio,  and  quartz),  shale,  zincbleudc,  and  iron  oxide. 

Limestone  

Limestone  
I/kncstone  

CX1OH. 

*  Microscopically  examined. 


STOEEY  AND  LYON  COUNTIES. 


The  only  mines  of  importance  in  these  counties  are  1ho.se  of  the  Comstock  lode,  of  which  sufficient  mention  has 
been  made.    There  are,  however,  other  silver-bearing  veins  in  eruptive  rocks  of  this  region,  though  none  which 
yielded  large  and  steady  profits. 


STOREY  AND  LYON. 


Mine. 


T11E   COS18TOCK 


Ore  and  gangne. 


Foot. 


Hanging. 


Auriferous  quartz . 


Qnartz,  argentitc,  native  silver,  and  gold,  occasionally 
stephanite,  polybasite,  etc.,  iron  and  copper  pyrile, 
rarely  calcite. 


.  Diorito  * . 


Utah 

Peytona 

Sierra  7,  evada 

Union  Consolidated 

Mexican 

Opbir 

C;.,iiurnia 

I  'nu'-nlidnted  Virginia 

Belcher 

(ioiild  fe  Curry 

I 1  ul"  &  Nnrcross 

Clir.llar 

Potosi  

Bullion 

Exchequer 

Alpha 

Challenge 

Confidence 

Yellow  Jacket 

Kentnck 

Crown  Point 

I't-lrlu-v 

Overman...  -.do Quart z-porpbyry,*  diorite,* 


Dlorite  * 
...do*.. 


Qnartz,  argentite,  native  silver,  and  gold,  occasionally   J 
stephanite,  polybaaite,  etc.,  iron  and  copper  pyrite,    >  Black  slate " 
rarely  calcite.  ) 


A  Ha ...  do 

JiiMiei; :  Rebellious  silver  ores  in  calcareous  ganguc  Qn:  rtz- 


*  Microscopically  examined. 


and  metamoipbics.* 
.do 


"auclmeta- 


Diorite  • 
...do*.. 


Diabase* 


Diablo" 


Character  of 
deposit. 


Vein. 
Do. 


Do. 


Diabase  in  part  * . 


Diorite*  ami  andi'nit«* 
Diont.' '  and  andesite  * 


Do. 


Do. 


Do. 
Do. 


38 


PRECIOUS  METALS 


WHITE  PINE  COUNTY. 

The  famous  deposits  of  the  White  Pine  district  consist  largely  of  horn-silver  in  irregular  bodies  in  Devonian 
limestone.  The  chloride  is  accompanied  by  some  lead  minerals,  however,  and  these  predominate  in  the  deposits  of 
the  base  metal  range  near  by.  It  is  possible  that  the  horn-silver  of  the  Ebcrhardt  &  Aurora  is  a  product  of  the 
decomposition  of  argeutitc,  and  it  is  distinguished  from  ordinary  occurrences  in  limestone  by  the  presence  of  large 
quantities  of  quartz  gangue,  but  the  admixture  of  lead  minerals  suggests  that  the  ore  bodies  may  be  nearly  related 
to  the  class  of  which  the  Eureka  deposits  are  representative.  There  are  also  veins  in  the  county  associated  with 
slate  and  massive  rocks  as  well  as  limestone.  These  for  the  most  part  carry  copper,  besides  silver  and  some  gold". 
In  the  Eobinson  district  there  are  mines  the  ore  of  which  is  smelted  for  copper.  They  carry  gold  and  silver  in 
addition  to  the  copper,  and  may  represent  extreme  cases  of  the  miueralogical  association  last  mentioned. 

WHITE  PCfE. 
[NOTE. — Determinations  in  parenthesis  are  given  on  the  authority  of  the  experts.] 


Mine, 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit 

Foot 

Hanging. 

CHEEKY  CREEK. 

Diorite  (?) 

Contact  vein. 
Vein. 

Contact  vein. 

Vein. 

Impregnation. 
Do. 

Stir 

Slate     

Slate 

Ticknp 

Copper  carbonates,  sulpbnrets,  (horn-silver.and  quartz) 
Probably  tetrahedrite,  with  carbonates  

Limestone  

....do... 

KEWAHK. 

Limestone  

Limestone. 
Limestone  

WAliD. 

Probably  stromeyerite  and  snlpbantimonifles,  quartz, 
calc-Bpar,  pyriie,  zincblende,  and  cbalcopyrite. 

Slato,  limestone,  and  prob- 
ably granite. 

WHITE  PINE. 

....do  

....do  

The  remaining  counties  are  of  little  importance  at  present.    Washoe  is  one  of  the  oldest  mining  counties,  and 
contains  base  metal  mines  and  silver  veins,  but  its  product  is  now  very  small,  while  the  resources  of  Douglas, 
„  Ormsby,  and  Koop  are  undeveloped. 

• 

GEOLOGICAL  SKETCH  OF  UTAH. 

In  northern  Utah  the  Wahsatch  range  trends  approximately  north  and  south.  It  ends  to  the  south  about 
latitude  39°  30',  but  is  nearly  continuous  with  the  western  edge  of  the  high  plateau,  which  sweeps  to  the  westward 
as  the  latitude  diminishes.  Together  they  form  the  eastern  limit  of  the  Great  Basin,  and  divide  Utah  into  two 
unequal  parts,  of  which  the  western  is  the  smaller.  These  two  portions  of  the  territory  differ  greatly.  The  Great 
Basin  in  Utah  is  characterized  by  the  presence  of  the  Great  Salt  lake  and  extensive  areas  of  especially  desolate 
alkaline  desert,  as  well  as  by  the  system  of  mountain  ranges  mentioned  in  the  description  of  Nevada.  To  the  east 
of  the  basin  lies  an  elevated  area,  of  which  the  distinguishing  characteristic  is  the  horizontally  of  its  strata.  The 
general  character  of  this  region  is  that  of  a  great  undulating  plain,  though  it  is  not  utterly  devoid  of  hills.  Its  soft 
surface  is  deeply  carved  by  modern  streams  into  fantastic  pinnacles  and  bluffs,  which,  added  to  the  prevailing  extreme 
barrenness,  gives  it  a  strange  aspect,  and  a  large  portion  of  it  has  received  the  significant  name  of  "bad  lands". 
This  plain  is  broken  in  latitude  40°  30'  by  the  great  eastern  and  western  ranges  of  the  Uintah  mountains,  which  are 
150  miles  long,  and  rises  at  its  culminating  point,  Emmons  peak,  to  an  elevation  of  about  13,700  feet.  It  is  unlike 
any  other  range  in  America,  being,  in  fact,  a  lofty  forest-covered  plateau,  from  which  rise  bare  rocky  peaks, 
composed,  like  the  plateau,  of  nearly  horizontal  strata.  It  divides  the  Green  River  basin  from  the  great  plateau 
basin  of  the  Colorado,  but  is  cut  through  by  the  Green  river.  These  two  areas  share  the  characteristics  just 
described. 

The  mineral  resources  of  Utah  are  extensive  and  varied,  and  comprise  lead,  silver,  gold,  copper,  coal,  iron, 
salt,  sulphur,  etc. 

All  the  government  surveys  have  done  more  or  less  work  in  Utah,  but  so  far  as  the  mining  regions  are  concerned 
the  chief  sources  of  information  are  the  publications  of  the  exploration  of  the  fortieth  parallel  and  the  geological 
volume  of  Captain  Wheeler's  survey.  Dr.  J.  8.  Newberry  has  printed  important  papers  on  the  subject,  and  Mr.  G. 
JL  Gilbert  has  published  a  paper  on  lake  Bonneville.(a) 

The  Wahsatch  forms  the  boundary  between  two  distinct  geological  regions.  At  the  close  of  the  Carboniferous 
the  western  portion  of  the  Great  Basin  (including  the  area  of  the  Wahsatch)  was  raised  above  the  level  of  the 


a  Second  Annual  Report  Director  United  States  Geological  Survey. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  39 

• 

ocean,  a  position  which  it  maintained  throughout  the  Mesozoic  era.  The  regi»n  to  the  east  of  the  Wahsatcli.  on  the 
other  hand,  remained  undisturbed  during  the  Trias  and  Jura,  and  underwent  only  gentle  changes  of  elevation 
during  the  Cretaceous.  The  post-Jurassic  upheaval,  which  folded  up  the  Sierra  Nevada  and  the  Basin  ranges, 
probably  also  had  its  effect  upon  the  Wahsatch,  but  extended  no  farther.  At  the  end  of  the  Cretaceous  a  vast 
upheaval  took  place  in  the  heart  of  the  country,  by  which  the  whole  system  of  the  Rocky  Mountain  ranges  was  raised 
substantially  to  its  present  position,  displacing  the  great  gulf  which  had  hitherto  occupied  this  area.  In  this  uplift 
the  Wahsatch  was  involved,  as  is  known,  by  the  plication  of  the  Cretaceous  strata  ou  its  eastern  slope;  but  the  effect 
of  the  movement  is  not  traceable  further  to  the  west.  The  Wahsatch  range  thus  belongs  geologically  both  to  the 
system  of  the  Basin  ranges  and  to  the  Rocky  Mountain  system,  and  forms  a  broad  boundary  wall  between  the  two. 

A  great  fault  has  taken  place  at  the  western  side  of  the  Wahsatch,  which  forms  its  foot  wall.  Had  erosion  not 
modified  the  range,  it  would  be  seen  to  consist  of  Mesozoic  and  earlier  strata  continuous  with  those  of  tlie  country 
east  of  it  but  bent  upward  near  the  fault-plane,  so  that  on  the  west  of  the  crest  there  would  be  a  gigantic  cliff, 
cutting  the  strata  nearly  at  right  angles,  while  the  eastern  face  would  slope  steeply  away  from  the  crest,  but  would 
gradually  flatten  and  pass  over  into  the  nearly  horizontal  surface  of  the  plateaus.  To  the  south  of  fhe  Wahsatch 
the  plateau  country  was  also  elevated  at  the  close  of  the  Cretaceous,  but  its  uplift  was  not  attended  or  followed  by 
any  horizontal  thrust  sufficient  to  flex  the  strata  near  the  line  of  upheaval  into  mountains.  The  Uintah  range  likewise 
dates  from  the  post-Cretaeeous  uplift,  and  indicates  a  northern  and  southern  compression,  for  its  character  is  that  of 
a  broad  anticlinal.  Since  the  post  Cretaceous  there  have  been  further  orographical  changes,  though  none  which  have 
introduced  new  topographical  features  of  importance. 

The  great  Wahsatch  fault  is  a  feature  of  the  geology  of  Utah  which  has  probably  had  an  important  influence 
on  many  of  its  geological  phenomena,  including  that  of  mineral  deposition.  The  geologists  of  the  fortieth  parallel 
have  shown  that,  as  far  back  as  the  Archsean,  a  fault  occurred  along  the  range  coinciding  for  the  most  part  with  its 
present  western  foot.  Renewed  dislocation  on  the  same  jjlane  occurred  at  the  close  of  the  Cretaceous  or  early  in 
the  Eocene,  again  in  the  Quaternary,  and  the  fault  appears  to  be  in  progress  even  at  the  present  day,  for  so  fresh 
is  the  most  recently  exposed  surface  that  vegetation  has  not  had  time  to  clothe  it.  The  observers  draw  the  inference 
that  such  fractures  in  the  earth's  crust  always  remain  lines  of  weakness,  liable  on  comparatively  slight  occasion 
to  further  dislocation. 

During  the  Trias-Jura  the  gulf  or  inland  sea,  of  which  the  Wahsatch  formed  the  western  shore,  was  shallow  in 
the  northern  and  central  portions  of  Utah,  and  the  sediments  consist  of  sandstones  and  shales,  often  cross-bedded 
by  the  action  of  currents.  Numerous  pools  seem  also  to  have  been  cut  off'  from  the  main  body  of  the  water,  and  thus 
to  have  been  exposed  to  evaporation.  The  result  is  seen  in  frequent  gypsum  deposits,  which  are,  for  the  most  part, 
thickest  at  the  center  and  thin  out  toward  the  edges.  Such  conditions  are  not  favorable  to  marine  life,  and  a  very 
large  part  of  the  strata  representing  the  Trias-Jura  contain  only  fragments  of  vegetation  from  surrounding  coasts. 
At  the  southern  end  of  the  territory  during  the  Jurassic  the  sea  was  deep  and  deposited  calcareous  sediments. 

During  the  Cretaceous  the  water  was  for  the  most  part  shallow  toward  the  north,  and,  in  consequence  of  gentle 
oscillations  in  level,  land  and  sea  frequently  alternated  on  the  eastern  side  of  the  Wahsatch.  Portions  of  the 
country,  however,  were  maintained  long  enough  above  sea-level  to  permit  of  the  growth  of  an  extensive  flora,  and, 
as  a  consequence,  the  Cretaceous  strata  are  marked  by  the  presence  of  numerous  carbonaceous  beds,  which  often 
contain  coal  seams  of  fair  thickness.  In  southern  Utah  the  Cretaceous  sea  at  certain  points  was  deep,  but 
throughout  the  plateau  area  most  parts  of  it  were  shallow. 

After  the  post-Cretaceous  uplift,  and  throughout  the  Tertiary,  the  region  east  of  the  Wahsatch  was  occupied  by 
grAit  fresh-water  lakes,  the  sediments  of  which  toward  the  north,  and  especially  near  the  Uintah  range,  are  deposited 
uncouformably  on  the  Cretaceous.  In  tkis  region  they  are.  also  unconformable  among  themselves,  showing  that 
orographical  changes  took  place  during  their  deposition.  In  southern  Utah,  however,  the  Tertiary  fresh-water 
strata  appear  to  show  no  non-conformity  either  with  one  another  or  with  the  underlying  Cretaceous.  It  is  these 
fresh-water  Tertiaries  which  have  been  modeled  by  modern  streams  into  the  fantastic  forms  characteristic  of  the 
bad  lands.  Several  large  lakes  existed  in  the  Great  Basin  during  this  era,  and  similar  conditions  prevailed  through 
the  Quaternary,  modified  only  in  more  recent  times  by  slight  orographical  changes  and  by  greatly  increased 
evaporation.  The  great  Quaternary  lake  of  Utah  was  Bonneville,  the  kistory  of  which  has  been  studied  by  Mr. 
G.  K.  Gilbert.  According  to  that  geologist  the  present  dry  period  in  the  Great  Basin  is  not  the  only  one  which  it 
has  experienced.  A  long  remote  period  of  drought,  daring  which  the  lake  sometimes  nearly  or  quite  dried  up,  was 
succeeded  by  a  long  wet  period,  in  which,  however,  there  was  an  insufficient  supply  of  water  to  permit  an  overflow. 
Next  oame  a  time  so  «iry  that  the  lake  altogether  disappeared,  and  then  one,  of  so  much  precipitation  as  to  allow  of 
discharge  by  overflow.  This  was  followed  by  the  present  epoch,  in  which  the  area  of  water  has  been  reduced  to  that 
of  the  Great  Salt  lake  and  the  smaller  bodies  south  of  it.  (a) 

The  eruptive  rocks  of  western  Utah  are  the  same  as  those  of  Nevada,  and  are  represented  by  Arcluvan  granites, 
Mesozoic  diorites,  diabases,  etc.,  and  Tertiary  or  post-Tertiary  audesites,  rhyolites,  and  basalts.  According  to  Mr. 
Hague,  no  true  trachytes  are  found  among  the  rocks  collected  in  Utah  by  the  exploration  of  the  fortieth  parallel. 


a  Second  Annual  Report  of  Ilie  I>ircutvr  of  tlie  United  Statfn  Geological  Surrey. 


40  PRECIOUS  METALS. 

An  interesting  series  of  rooks,  locally  called  syenitic  porphyries,  has  been  collected  in  the  West  Mountain  district, 
Oquirrh  range,  by  the  census  expert,  which  seem  to  be  highly  augitic  granite-porphyries.  As  in  Nevada,  there  is 
an  intimate  relation  between  the  ore  deposits  and  occurrences  of  eruptive  rocks,  the  former  seldom  being  found 
except  in  the  immediate  neighborhood  of  the  latter. 

Metallic  ores  are  rare  east  of  the  Wahsatch  and  in  the  plateau  country,  where  indeed  Tertiary  strata  occupy 
much  of  the  surface.  In  southern  Utah,  however,  the  Triassic  sandstones  carry  silver  and  copper,  and  especially 
rich  strata  of  this  age  form  the  famous  silver  reefs  near  Leeds.  To  the  west  of  the  Wahsatch  and  along  the  edge 
of  the  high  plateau  a  series  of  ore  deposits  is  found  from  one  end  of  the  territory  to  the  other,  forming  a  true 
mineral  belt.  All  of  these  are  associated  with  Palaeozoic  strata,  which,  however,  proves  nothing  as  to  the  age  of 
the  deposits ;  indeed,  it  is  known  that  some  of  them  must  be  Tertiary  or  post-Tertiary.  It  seems  extremely  probable 
that  these  ore  deposits  owe  their  existence  to  the  solfataric  action  accompanying  the  eruption  of  massive  rocks,  and 
that  the  points  where  these  reached  the  surface  were  determined  by  the  line  of  disturbance,  of  which  the  great 
Wahsatch  fault  is  the  most  striking  manifestation.  At  all  events,  it  is  a  fact  that  the  western  edge  of  the  post- 
Cretaceous  uplift  is  marked  in  Utah  by  an  immense  number  of  deposits.  It  has  been  pointed  out  on  a  preceding 
page  that  there  is  a  strong  analogy  between  the  geological  relations  of  the  mineral  belt  of  Utah  and  those  of 
California.  There  are  ores  in  the  Basin  ranges  of  Utah  as  well  as  near  the  Wahsatch,  and  particularly  in  the 
Oqnirrh  mountains,  which  lie  to  the  west  of  Utah  lake.  These  are  very  similar  to  the  deposits  in  the  kindred  ranges 
of  Nevada. 

The  prevailing  type  of  the  ore  deposits  in  Utah  consists  of  more  or  less  regular  bodies  of  argentiferous  lead 
ores  associated  with  limestone,  and  usually  accompanied  by  eruptive  rocks.  The  original  form  of  the  ore  was 
probably  in  all  such  cases  galena,  which  in  a  majority  of  instances  has  yielded  to  decomposition  processes  for  a  long 
distance  from  the  surface,  and  is  now  replaced  by  carbonate,  sulphate,  and  other  secondary  minerals.  Of  such 
occurrences  the  Horn  Silver  mine  is  an  excellent  type  and  an  important  instance.  The  deposit  worked  by  this 
mine  lies  between  a  foot  wall  of  dolomitic  limestone  and  a  hanging  wall  of  rhyolite.  The  nature  of  this  lava  is 
proved  by  microscopic  slides  in  the  census  collection.  Small  masses  of  galena  occur,  but  the  prevalent  mineral  is 
the  sulphate  which  has  formed  in  consequence  of  oxidation  of  the  galena.  It  is  a  significant  fact  that  heavy  spar 
is  one  of  the  gangue  minerals,  but  occurs  only  near  the  rhyolite.  The  same  district  shows  other  volcanic  rocks.  An 
augite-audesite  is  found  near  the  Horn  Silver  inine;  and  the  Carbonate  mine,  near  by,  is  associated  with  a  hornblende- 
andesite  of  so-called  "  trachytic"  habitus  similar  to  the  Mount  Eose  hornblende-andesite  of  the  Washce  district. 

The  veins  in  Utah  which  are  associated  with  slates  or  quartzites  do  not  commonly  carry  a  preponderance  of 
lead  ores,  but  are  cupriferous  and  sometimes  auriferous ;  the  gangue  in  such  cases  is  also  generally  quartz.  Of  such 
mines  the  Ontario  Is  much  the  most  important. 

The  Ontario  mine  in  the  Uintah  district,  Summit  county,  is  a  strong  vein,  several  feet  wide.  Its  ores  are 
zincblende,  galena,  fahlerz,  and  pyrite,  with  some  horn-silver  and  copper  carbonate  in  a  quartz  gangue.  The  walls 
are,  in  the  main,  quartzite,  but  at  400  feet  a  porphyry  was  struck  near  the.vein  which  appears  at  lower  levels  in 
contact  with  the  vein,  and  it  is  thought  will  replace  quartzite  as  the  hanging  wall.  Unfortunately  the  specimens 
of  this  porphyry  received  are  too  much  decomposed  to  make  determination  possible.  It  is  full  of  pyrite,  and  has 
manifestly  been  subjected  to  solfataric  action.  The  Ontario  is  one  of  the  richest  mines  in  the  country.  Its  ore  is 
treated  by  roasting  in  a  Stetefeldt  furnace  and  amalgamation. 

The  sandstones  of  southern  Utah  and  the  adjoining  regions  carry  a  very  unusual  form  of  ore  deposits, 
consisting  of  impregnations  of  silver  and  copper,  partly  native  and  partly  as  sulphides.  Much  of  the  silver  sulphide 
has  also  been  converted  into  chloride.  The  age  of  these  sandstones  was  determined  by  Professor  J.  Marcou,  and 
subsequently  by  Dr.  J.  8.  Newberry,  as  Triassic — a  determination  confirmed  by  Messrs.  Gilbert  and  Howell.  (a) 
The  geological  information  which  has  been  published  on  this  subject  is  very  largely  due  to  Dr.  J.  S.  Newberry.  (b) 
After  having  described  the  peculiar  character  of  the  Triassic  sea  in  this  portion  of  the  continent  and  mentioned  the 
well-known  facts  regarding  the  silver  contents  of  ordinary  sea- water,  this  geologist  states  his  opinion  as  to  the  origin 
of  the  silver  and  copper  in  the  sandstones  as  follows : 

Near  the  Utah  shore  of  this  Triassic  basin  the  water  would  seem  fo  have  been  more  highly  charged  than  elsewhere  with  silver, 
though  it  was  also  the  associate  of  the  more  abundant  copper  in  New  Mexico,  the  Indian  territory,  and  Texas.  Doubtless  this  silver 
was  brought  up  in  springs  on  the  old  land  from  the  same  sources  which  furnished  so  large  an  amount  of  silver  to  the  fissure  veins  formed 
there  long  after.  Near  the  old  shore  the  drift-wood  brought  down  by  the  draining  streams  and  scattered  by  the  shore-waves,  when 
buried  in  the  accumulating  sediment,  became  more  or  less  replaced  by  copper  and  silver,  precipitated  by  the  reducing  action  of  organic 
matter  which  is  manifested  in  so  many  different  ways.  The  quantity  of  silver  in  some  of  the  bays  and  estuaries  carried  by  draining 
streams,  perhaps  fed  in  part  by  mineral  springs,  may  have  been  greater  than  that  in  most  parts  of  the  water-basin,  and  hence  the 
sediments  formed  there  hold  a  quantity  larger  than  the  average.  We  find  the  same  variation  in  the  distribution  of  copper  farther  east. 
In  «ome  places  it  was  so  abundant  that  it  was  not  all  taken  up  by  the  decaying  wood,  but  formed  concretions  of  sulphide  in  the  sand  or  , 
clay. 

**  »  »«»«, 

The  ores  of  silver  and  copper  plainly  existed  as  solutions,  which  saturated  the  sand  when  it  was  collected  and  deposited  the 
sulphides  with  sandstone  after  the  mechanical  action  which  transported  the  sediment  was  at  an  end.  All  this,  however,  was  within  the 
Triassic  age,  while  the  water  was  shallow  and  highly  charged  with  mineral  matters. 


a  Surveys  West  of  the  lOQIh  Meridian,  vol.  2,  p.  176.  b  See  especially  Engineering  and  Mining  Journal,  vol.  31,  p.  6. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


41 


He  states  later  in  the  same  article  that  he  regards  it  as  possible,  though  uot  probable,  that  in  some  places  the 
porous  sandstones  of  the  Trias  were  penetrated  by  solutions,  from  which  the  sulphides  of  copper  and  silver  were 
precipitated. 

The  undisturbed  condition  of  some  of  the  sandstones  is  certainly  an  argument  in  favor  of  the  supposition  that 
the  ore  was  deposited  with  the  sandstone,  but  there  are  considerable  difficulties  involved  in  its  acceptance. 
Common  sea-water  will  dissolve  only  an  extremely  small  amount  of  silver  salts,  though  saturated  solutions  of  salt 
are  capable  of  dissolving  silver  chloride  in  considerable  quantities.  If  the  Triassic  sea  held  the  silver  in  solution, 
it  can  only  have  been  charged  with  the  metal  after  isolation  from  the  main  ocean  and  concentration  by  evaporation ; 
but  it  is  difficult  to  suppose  this  combination  of  conditions  prevailing  over  wide  areas.  The  deposits  of  commern 
in  Ehenish  Prussia  present  very  strong  analogies  to  those  of  Silver  Keef,  but  there  it  is  an  argentiferous,  though 
otherwise  very  pure  galena,  which  is  disseminated  through  sandstone.  There  are  strong  chemical  objections  to 
supposing  this  galena  to  have  been  deposited  directly  from  the  ocean,  or  even  from  a  land-locked  basin  of 
concentrated  sea- water ;  yet  a  satisfactory  theory  would  give  an  account  of  it  as  well  as  of  the  Utah  silver.  The 
theory  of  impregnation  of  the  sandstones  by  solution  presents,  in  my  opinion,  fewer  difficulties.  It  is  not  easy  to 
see  why  the  replacement  of  organic  matter,  such  as  wood,  by  the  metals  would  not  occur  as  readily  from  an 
ascending  solution  as  from  sea-water,  while  ascending  solutions  would  certainly  favor  the  formation  of  the 
considerable  nodules  of  ore  sometimes  found  in  the  sandstone.  May  these  deposits  not,  after  all,  be  chemically 
and  physically  analogous  to  ordinary  veins,  though  so  different  from  them  structurally  ?  It  is  supposed  that 
precipitation  takes  place  in  veins  where  there  is  room  for  deposition,  and  where  at  the  same  time  relief  of 
temperature  and  pressure  or  chemical  action,  especially  that  of  organic  matter,  induce  precipitation.  In  ordinary 
rocks  such  conditions  are  to  be  found  mainly  in  fissures,  but  in  sandstones,  particularly  such  as  carry  organic 
matter,  they  may  occur  anywhere,  and  the  presence  of  copper  or  lead  would  be  as  readily  accounted  for  as  that  of 
silver.  Dr.  Newberry  records  that  analyses  made  at  his  instance  by  Mr.  J.  B.  Mackintosh  shoflfcthat  the  silver 
in  some  of  the  sandstones  is  accompanied  by  selenium  in  considerable  quantities. 

The  number  of  workable  coal-seams  in  Utah  is  very  considerable.  Those  thus  far  opened  lie  for  the  most  part 
on  the  eastern  flank  of  the  Wahsatch,  or  not  far  from  the  western  edge  of  the  high  plateau,  and  while  search  for 
them  elsewhere  is  by  no  means  hopeless,  these  localities  seem  most  likely  to  show  good  seams.  Both  Cretaceous 
and  Tertiary  beds  are  said  to  occur,  (a)  and  some  of  them  are  reported  to  present  very  unusual  qualities  for  coals  of 
such  recent  date,  not  crumbling  on  exposure,  containing  a  very  small  amount  of  water,  and  yielding  strong  coke. 
The  great  value  of  such  beds,  at  an  immense  distance  from  the  well-explored  coal-fields  of  the  Carboniferous  era, 
is  patent. 

In  the  appendix  will  be  found  a  report  on  the  mining  industries  of  Utah  by  Mr.  D.  B.  Huntley,  who  filled  the 
office  of  special  expert  for  the  territory.  This  paper  describes  the  mineral  resources  in  so  much  detail  that  any 
special  notes  ou  the  counties  are  unnecessary  here. 

BEA.VEK. 

. — DeterminatioBS  in  parentheses  are  given  on  the  authority  of  the  experts.] 


WAL 

LS. 

Character  of 

Foot 

Hanging. 

deposit. 

BRADflHAW. 

Irregular  bodies. 

8AN  FRANCISCO. 

aragonite,  and  limonite,  (manganese  oxide,  native 
sulphur). 

Rhyolite  *  

Chimney. 

noysito,  prouslite,  (pyrarjiyrite).  oerarjryrite,  argen- 
tito  also  occur  with  calcite,  quartz,  and  buiite. 

Hornblende-andeaite  *  

Vein. 

Irregular  bodie*. 

Limestone  and  slate  

Pipe*. 

STAB. 

fluorspar). 

Black  limestone. 

Dolomitic  limestone  

Chimney. 

Siliceous  limestone. 

Kebel 

Galena  cerussite  free  sulphur,  gypsum,  and  quartz, 

Crystalline  limestone  

Crystalline  limestone. 

(limonito). 

Granite  * 

Dolomitic  limestone  

Chimney* 

silver). 

Microscopically  examined. 


a  E.  E.  Howell  in  Surveys  West  of  the  IWth  Meridian,  vol.  3,  p.  278. 


42 


PRECIOUS  METALS. 


(NOTE. — Determinations  in  parentheses  are  given  «n  the  authority  of  the  experts.] 


Mine. 

Ore  and  gangue. 

WALL*. 

Character  of 
deposit. 

Foot 

Hanging. 

TDiTlO. 

(Porphyry)  

(Porphyry)  

Pipes. 
Mineral  bolt. 

Vein. 
Do. 
Irregular  massed. 

Vein. 
Vein. 

Vein. 
Do. 

Do. 

British 

(Copper   minerals,   limonito,   calcito,   quartz,   rarely 
gold,  and  manganese  oxide.) 

Quartzose,  carrying   limonito  and   lead,  probably  as 
cerussit*,  (copper  carbonates  and  sulphides). 

Erubescito,  auglesito,  pyrito,  mispickel,  quartz,  (lim- 
ouite). 

Galena  nnd  its  decomposition  products,  copper  stains, 
hematite,  quartz,  calcito,  (lead  ocher,  gold,  horn-sil- 
ver, auil  zincbleudf). 

Bismnthite  (argentiferous). 
Siliceous  and  ferruginous  rock  (carries  bismuth  and 
silver). 
Ferruginous  quartz,  calcite,  and  cenissite  (?)  

Carisa          

3'robably     dacito,  *     (lime- 
atone). 

Hornblende-andesite*  

Probably      dacite,  *    (lime- 
stone). 

norublende-audesite  *  

Eureka  Hill                       

Siliccoua  limestone  

Indetcrminably  decomposed 
massive  rock. 

Andesite,    (?)     decomposed 
and  pyritiferous. 

Siliceous  limestonn  

Indetertninably  decomposed 
massive  rock. 

Andosito,    (?)     decomposed 
and  pyritiferous. 

Golden  Bell    

Cuprite,  pyromorphite,  copper  carbonates,  quartz,  cal- 
cite, pyrolusite,  (liinouite,  argentite,  and  horn-sil- 
ver). 

Limestone. 
Diorito* 

Anglesite,  iron  oxide,  and  quartz. 

Galena,  ceruasite,  qnartz,  (limonite  and  silver,  prob- 
ably as  argentite). 

Argentiferous  pyrolusite,  (galena,  gold,  and  copper)  .  .  . 
Galena,  cernssite,  calcite,  and  quartz. 

Diorite* 

Park                                  

Rising  Sun     .         

(Granite)  (?) 

(Granite)  (?) 

• 

*  Microscopically  examined. 

PIUTE. 
[NOTE.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


OHIO. 

Bullv  Bov 

Vein 

MOUNT  BALDY. 

Beer  Trail  

hedrite,  chnJcopyrke,  chalcosite,  aad  quartz). 

Qunrtzite    

Green-Eyed  Monster  

feuite,  quartz,  (lead  ochor  and  copper  sulphides). 
do  .... 

do  

do 

Do 

Pluto 

*  Microscopically  examined. 

SALT  LAKE. 
[NOTB. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


BIO  COTTON-WOOD. 

Anellie  

Melaconite  and  malachite,  (lead,  silver,  and  gold)  .  

Gulena,  limonite,  copper  stains,  and  calcite,  (cerussite 
and  manganese  oxide). 

Galena,  limonite,  calcite,  pyrolusite,  and  quartz 

(Limestone). 
Limestone. 

do 

Vein. 

Bedded  vein. 

Bedded  vein. 
Vein. 

Belt. 
Vein. 

Vein. 
Vein  or  belt 

Antelope  &  Prince  of  Wales. 
Butto  

do 

Carbonate  

Galena,  ceruasite,  limonite,  and  calcite   

Galena,  cerussite,  malachite,  pyrite,  quartz,  calcito, 
talc,  (manganese  oxide  and  lituonite). 

Galena,  cerussite,  copper  stains,  pyrolusite,  nnd  iron 
oxide. 

Cerussite,  plumbic  ochcr,  auglesite.  and  tuilcite  

Galena,    cerussite,    plumbic    ocher,  (copper   stains, 
quartz,  and  limouite). 

(Galena,  ceruaaite,  limouite,  and  quartz)  

(Galena),  corussite,  angleaite,  and  pyrolaaite. 

(Galena),  cerussite,  wnlfenito,  cuprite,  malachite,  py- 
rolusite, and  limonite. 

Galeua  and  quartz. 

Galena,    cerusaite,    anglesito,    limonite,    calcareous 
gaugue,  (manganese  minerals). 

Galena,  dufrenoysite,  pyrite,  calcareous  gangue,  (tet- 
rahedrite,  zlncblende,  and  qnartz). 

(Galena  and  cerusaite) 

Dolomitic  limestone. 

Maxfleld  

Ophir  

Blue  limestone. 
Limestone. 

Keed  &  P>enson  :  

Silver  Mountain  

Thor  &  Bright  Point  

Quartette  

Limeatone  and  diorito  *  .... 

LITTLE  COTTOXWOOll. 

Cincinnati   

Limestone  and  diorite.  * 

City  Kocks 

Dexter  

Emma  

Emily  

Equitable  

(Limestone). 
(Limestone  and  sandstone). 
Limestone. 

Evergreen  

(Galena,  cerussite,  limonite,  and  copper  carbonates).. 

Cernsaite,   copper  stains,   limonite,  and  manganese 
minerals. 

(Limestone  and  sandstone)  .  . 

Grizzly  

Louise  

North  Star  

Galena,  cernasite,  and  wnlfenite  ... 

Limestone  ... 

Limestone  .  . 

GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


43 


SALT  LAKE— Continued. 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

UTTLE  COTTOXWOOD—  COnt'd. 

Galena,  cernssito,  plumbic  ocher,  wad,  enargite,  py- 
rite,  rhaleopyrite,  malachite,  nian-iwite,  calcareous 
gangue,  (oxide  of  manganese  and  quartz). 

(Quartzite)  

(Qnartzite)  

Vein. 

Vein. 
Vein. 

Vein. 

Belt. 

Vein. 

Bedded  vein.  (?) 
Vein. 
Bedded  vein. 
Belt 
Do. 

Vein. 
Bedded  vein. 

Vein. 

Vallejo 

Galena,  corussito,  aniilt-site,  copper  stains,  limonito, 
ban.  s  man  u  iU-,  and  wuliV-nite. 

Cerussite,  limonito,  probably  horn-silver. 

Galena,  /incblende,  copper  pyrite,  (limonite,  silver, 
and  gold). 

Dolomite. 
(Black  limestone)  

WEST  IfOUXTAIS. 

Highland  Boy 

Qnartzite  

Limestone. 
Siliceous  limestone  

Galena,  (gold),  iron  and  copper  pyrites,  cernssite,  limo- 
nite, quartz,  and  copper  stains. 

do  

Granite-porphyry*  

Granite-porphyry.  ' 

(Between  granite  and  quartz- 
ito.) 

(Quartzite). 
Qnartzite  

Orpiment  and  realgar. 

(Between  granite  and  quartz- 
ito.) 

Galena,  reniasito,  iron  and  copper  pyitftes,  malachite, 
limonite,  nud  quartz. 

Galena,  cernssite,  argent  itot  pyrar^vrite,  rhodocrosite, 
zincblendo,  quartz,  bartte,  (Dornlte,  culuite). 

do          

Aujritic        granite    •    por- 
phyry. (!)* 

Anuitic        granite    •    por- 
phyry. (?)* 
Qnartzite  

Stewart  No.  2  

Gold,  quartz,  limonite,  (silver  and  copper  carbonate)..    (Unknown)  

....do  

/OimrtiitRl 

Quartzite  •-  Quartzito  

Galena,  binnite,  zincblende,  pyrite,  cerussite,  quartz, 
iron  oxides,  (ruby  silver  and  native  silver). 

Victor 

(Quartzite)  (Onartzite)  

Galena,  dufrenoysite,  iron  and  copper  pyrites,  cerns- 
site, limonite,  zinc-vitriol  efflorescence,  native  sul- 
phur, (zincblende,   cubanite,  tetruhedrite,   calcite, 
and  gypsum). 

Galena,  cerussite,  iron  and  copper  pyrites,  mel&conite, 
limonite,  (boruite,  zincblendo,  and  quartz). 

Shale  

Quartzite  

*  Microscopically  examined. 

SUMMIT. 
[Nora. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


UIKTAH. 

Qnartzite  

(Said  to  be  porphyry)  

Vein. 

nese  oxide,  and  liiuonite. 

(Qnartzite)  

(Qnartzite). 

Qnartzite  

Qnartzite  and  indetermina- 

Vein. 

White  Pine1 

bleude,  (pyrite),  horn-silver,  malachite,  clay,  (quartz). 

ble  dioi  ite-like  porphyry. 
Diabase  (!)  

Do. 

Walker  &  Webster  

rahedrite,  argeutite,  'and  native  silver). 
Galena,  cerussite,  and  quartz. 

(Green  porphyry)  •.  

Vein. 

Woodside 

bonate,  manganese  oxide,  limonite,  and  quartz.) 
(Cerussite  angleaite  galena,  iron  oxide,  and  calcite)  

(Qnartzite)  

(Siliceous  limestone)  

Vein,  (t) 

TOOELZ. 
[UTOTB.— Determinations  in  parentheses  are  given  on  the  authority  cf  the  experts.] 


CAMPFLOTD. 

Carrie  Steele 

Stibnite  quartz  limonite,  (horn-silver  and  antimonial 

Limestone  

Siliceous  limestone  

Bedded  vein. 

OFHIR. 

silver). 

(Limestone)  

Bedded  vein. 

...do  

....do  

Bedded  mass. 

g 

do  

....  do  

Vein. 

.  '       ^ 

Limestone,  quartz-porphyry 

Slate  dike  

Chimneys. 

Sandstone  

Irregular  bodies. 

native  silver,  horn-silver,  aud  limouite.) 

Limestone  and  qnartzite  .... 

Indeterminable  porphyry  — 

Bedded  vein. 

Galena,  cerussite,  plattnerite,  (?)  pyrite,  (horn-silver, 

(Clay  shale,   close   to  lime- 

(Clay shale,  close  to  lime- 

Vein. 

chalcopyrite,  and  limouite). 

stone.) 
Fetid  limestone  

stone.  ) 
Calcareous  sandstone  

»o. 

and  ealcite. 
Cernssite,  limoait<',  and  calcic,  (the  limonite  is  argen- 

Limestone    

Limestone    

Do. 

tiferous). 

do 

do    

Pipes. 

RUSH  VALLEY. 

First  National Galena,  < 


f,  liinoirit«\  ; 


.  :;ud      (SilH-i-oiis  limestone) (Black  limestone) Bedded  vein 


Great  liasln CcnmMte,  limonite,  clay,  (argentiferous  galenn,  mala-     Limestone  . 

chite,  aud  manganese  minerals). 


Limestone 


44 


PRECIOUS  METALS 


UTAH. 
[NOTS.— Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


Mine. 

Ore  anil  gangue. 

WALLS. 

Character  of 
deposits. 

Foot. 

Hanging. 

AMKBICAX  F01IK. 

Galena,  pyrito,  qnartz,  (silver,  gold,  zinculcndo,  and 
copper  ore). 
Galena,  ccrussite,  zincblende,  pyrite,  limonito,  (silver, 
gold,  aud  quartz). 
(Galena,  cerussite,  limonite,  and  clay)  

(Quartzite)  

(Quartzite)  

Veto. 
Do. 

Do. 
Do. 

Do. 

Pipe*. 
Pocket*. 

Miller 

Shale  

(Limestone)  

"Wild  Dutchman  

Galena,  cerussite,  zincblendo,  quartz,  luuonite,  arsen- 
ical and  autiuionial  compounds. 

(Cernssito,  pyrite,  quartz,  Hmonite,  and  copper  stains.) 

Galena,  cerussite,  quartz,  limonite,  (pyrito  and  zino- 
blende). 

Limestone  
....do  

Limestone  
....do  

SILVER    LAKE. 
Milkmaid 

Quartzite  

(Quartzite) 

WAnsATcn. 

[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


BLUE  LEDGE. 

Granite  * 

Vein 

Wahaatch              . 

(Quartzite) 

(Quartzite) 

Do. 

SNAKE  CREEK. 

Malachite,  limonite,  calcito,  and  (qnartz)  

Granite*  

Granite*    

Vein. 

Shale 

m 

Utah            .         

Galena,  cerussite,  zincblende,  pyrite,  clay    and  (tet- 

Quartzite 

Vein. 

raliedrite). 

*  Microscopically  examined. 

WASHINGTON. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


HABKI8DURO. 

Magnesian  clay,  showing  flakes  of  silver.    Sandstone 

Bed. 

Barbee  &  Walker  

with  native  silver  aud  argvutite.    Fossil  plants  re- 
placed in  part  by  silver  and  horn-silver. 

Sandstono  with  native  silver  and  sulphurets,  (horn- 

Sandstone  

Do. 

Duffln                       

silver,  argentitc,  aud  lignite). 

do 

do 

Do. 

live  silver). 

do 

do 

Do. 

Leeds  

(silver,  argciitite,  and  lignite). 

do 

do                               

Do. 

Maud  

etable  matter.) 
do  

do 

do               

Do. 

Stormont  

do  

'...do    .. 

do  ..    

Do. 

GEOLOGICAL  SKETCH  OP  ARIZONA. 

In  the  latitude  of  Salt  Lake  the  Cordilleras,  as  Humboldt  called  the  entire  system  of  western  .North  American 
mountains,  occupy  a  breadth  of  over  1,000  miles.  In  the  latitude  of  Tucson  they  are  contracted  to  about  half  this 
width,  which  is  still  further  reduced  in  Mexico.  While  Nevada  occupies  only  a  portion  of  the  breadth  of  the  Great 
Basin,  Arizona,  though  no  wider,  includes  a  large  part  of  the  plateau  region,  the  southern  continuation  of  the  Basin 
ranges,  and  probably  a  portion  of  the  group  of  ranges  of  which  those  on  the  southern  coast  of  California  are 
members.  The  topography  is  thus  extremely  diversified  and  for  the  most  part  mountainous.  There  are  fertile 
valleys  and  well- wooded  mountains  in  the  territory,  but  the  prevalent  character  is  one  of  great  aridity,  and  in  the 
southwestern  portion  there  are  large  tracts  of  shifting  sands,  relieved  only  by  occasional  cactuses,  in  comparison 
•with  which  the  sage-brush  plains  of  the  Great  Basin  seem  areas  of  luxuriant  vegetation.  Arizona  is,  of  course, 
famous  for  its  mines,  which  produce  chiefly  gold  and  silver,  though  lead  and  copper,  particularly  the  former,  are 
rather  abundant,  and  will,  no  doubt,  be  exploited  on  a  large  scale  when  the  railroad  system  is  further  developed. 
Coal  also  occurs  in  considerable  quantities. 

A  number  of  geologists  have  visited  Arizona.  Dr.  Newberry  was  a  member  of  Lieutenant  Ivel's  expedition 
in  1857  ;  Major  Powell  and  Captain  Button  have  explored  the  Colorado  cafion  and  a  portion  of  the  plateaus,  and 
the  geologists  of  Captain  Wheeler's  survey  have  contributed  very  greatly  to  a  knowledge  of  the  main  features  of 
the  territory.  But  little  detailed  work,  however,  has  been  done  in  the  mining  regions,  aud  such  of  the  facts 
ascertained  as  are  appropriate  to  this  sketch  are  soon  told. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


45 


Northeastern  Arizona  belongs  to  the  Colorado  plateau,  of  which  about  one- third  falls  within  the  limits  of  the 
territory.  The  Arizona  plateaus  arc  for  the  most  part  nearly  level,  though,  as  in  Utah,  there  are  folds,  and  even 
ranges,  of  uplifted  mountains  at  long  intervals. 

The  southwestern  limit  of  the  plateaus  is  roughly  indicated  by  a  straight  line  running  northwest  from  a 
point  in  latitude  33°  30',  longitude  110°.  T-  tlie,  cast  of  this  imint  the  limiting  line  curves  eastward,  and  in  the 


adjoining  territory  of  Xcw  Mexico  turns  toward  the  north.     The  plateau  country  separates  two  systems  of  ranges 
which  meet  to  the  south  of  it.     Of  these  the  eastern  group  have  a  northern  trend  and  pass  into  the  Rocky  mountains 


46  PRECIOUS  METALS. 

of  Colorado.  The  western  group  trends  northwest,  and  is  continuous  with  the  Basin  ranges  of  Nevada.  Only  the 
latter  ranges  are  met  in  Arizona,  the  most  westerly  of  those  of  northern  trend  occurring  in  New  Mexico  just  easfc 
of  the  dividing  line. 

The  region  in  which  the  plateaus  and  the  two  systems  of  ranges  meet  is  characterized  by  an  immense  lava 
field  covering  between  20,000  and  25,000  square  miles. 

The  relations  of  the  two  systems  of  ranges  to  the  plateau  country  and  the  lava  fields  are  shown  in  the  sketch 
map  on  page  45,  borrowed  by  his  permission  from  Mr.  Gilbert's  report  on  the  geology  of  parts  of  Arizona  and 
New  Mexico,  to  which  our  knowledge  of  the  region  in  question  is  chiefly  due. 

Concerning  southwestern  Arizona  there  is  extremely  little  definite  information.  This  portion  of  the  territory 
is  mostly  composed  of  granites  and  crystalline  schists,  and  the  mountain  ranges  are  somewhat  irregular.  They 
appear,  however,  to  belong  to  the  same  structural  system  as  those  of  California  south  of  fort  Tejon,  with  which 
they  conespond  in  a  variety  of  details. 

In  Utah  the  edge  of  the  plateau  System  is  nearly  coincident  with  that  of  the  inland  Cretaceous  sea.  In  Arizona 
this  is  by  no  means  the  case,  the  surface  of  a  great  part  of  these  elevated  plains  toward  the  west  being  of 
Carboniferous  age,  and  the  Triassic  being  largely  represented  on  the  surface.  The  belt  of  Palajozoie  included  in 
the  plateau  country,  measured  from  the  southwestern  edge  of  the  latter,  averages  about  80  miles  in  width.  The 
ranges  trending  northwest  and  continuous  with  those  of  the  Great  Basin  are  also  composed  of  Palaeozoic  strata, 
except  where  the  Archaean  is  exposed  or  where  volcanic  rocks  hide  the  sedimentary  beds.  Captain  Button's 
investigations  have  established  that  the  Jura-Trias  strata  formerly  reached  the  edge  of  the  plateau  system  in 
Arizona  as  they  did  in  Utah,  but  have  since  been  removed  by  erosion.  This  is  .shown  by  the  presence  of  remnants 
of  these  beds  protected  by  lava  near  the  edge  of  the  plateau,  and  by  the  impossibility  of  reconstructing  their  surface, 
except  on  the  supposition  that  they  reached  this  line.  The  elevation  of  the  range  system,  judging  from  the  analogy 
of  the  Great  Basin,  is  most  likely  referable  to  the  post-Jurassic  disturbance  which  resulted  in  the  formation  of  the 
Sierra  Nevada.  Whether  the  Jura-Trias  beds  were  also  raised  above  water-level  along  this  line  at  this  time  is 
uncertain,  but  it  would  not  be  surprising  if  this  should  prove  to  be  the  case.  The  Cretaceous  sea  in  Utah  was 
shallow,  and  a  slight  post- J  urassic  elevation  would  have  thrown  its  shore  far  east  of  the  Wahsatch.  Such  a  change 
of  shore  line  may  have  taken  place  iu  Arizona  and  left  the  western  portion  of  the  plateau  dry,  or  the  shore  line 
may  have  been  nearly  coincident  with  the  edge  of  the  plateau,  aud  the  Cretaceous  deposits  afterward  removed  by 
erosion,  like  those  of  the  Jura-Trias.  The  disturbance  to  which  the  Arizona  ranges  is  due  extended  eastward  to  the 
edge  of  the  plateau  country,  and  the  post-Cretaceous  upheaval  which  raised  the  plateaus  extended  westward  to  the 
ranges,  exactly  as  was  the  case  in  Utah.  Iu  the  northern  part  of  the  territory  the  contact  between  the  Palaeozoic 
area  aud  the  crystalline  rocks  to  the  southwest  of  it  has  been  traced  for  a  long  distance.  This  line  probably  lies 
somewhat  to  the  northeast  of  the  original  edge  of  the  Palaeozoic,  but  at  no  great  distance  from  it.  That  a  portion  of 
these  strata  have  been  removed  by  erosion  is  indicated  by  the  occurrence  of  isolated  patches  near  the  main  area. 
The  most  remote  of  these  is  reported  as  occurring  in  the  Bill  Williams  Park  country,  aud  may  represent  a  gulf  in  the 
Palaeozoic  sea.  Though  the  southwestern  portion  of  the  territory  has  not  been  systematically  explored,  it  has  been 
traversed  in  many  directions  by  geologists  who  would  not  have  failed  to  recognize  Palaeozoic  strata  had  they 
encountered  them,  and  it  is  probable  that  they  are  absent  from  that  region. 

The  main  contact  between  the  Palaeozoic  aud  the  underlying  strata  is  laid  down  in  the  geological  maps  of  th» 
surveys  west  of  the  100th  meridian  continuously  from  Virgin  canon  to  Camp  Verde,  a  distance  of  170  miles. 
Farther  south  the  most  westerly  occurrences  of  Palaeozoic  shown  are  im  the  Pinal  mining  district  near  Florence  and 
in  latitude  32°  20',  longitude  100°  40'.  These  are  probably  near  the  edge  of  the  area,  though  there  is  some  evidence 
of  detached  patches  still  farther  to  the  south,  and  to  the  west  of  the  general  course  of  the  contact  so  far  as  traced. 
The  Chiricahui  range  Las  been  shown  by  Mr.  Gilbert  to  be  largely  made  up  of  Palaeozoic  strata,  aud  the  mines  of 
the  Tombstone  district  are  many  of  them  sunk  on  deposits  in  limestone.  In  this  region  limestones  can  hardly  be 
other  than  Paleozoic,  aud  they  are  reported  as  containing  Carboniferous  fossils. 

The  rocks  adjoining  the  Palaeozoic  to  the  southwest  are  unquestionably  Archaean,  for  their  relations  to  the 
Silurian  are  clear  at  a  great  number  of  points,  and  their  lithological  character  in  this  region  is  very  characteristic 
and  persistent.  There  seems  no  evidence  that  these  Archaean  rocks  have  been  covered  at  any  time,  except  where 
comparatively  small  patches  of  the  Palaeozoic  have  been  removed  by  erosion  near  the  contact.  Had  this  area 
formed  a  sea  bottom,  like  the  corresponding  region  to  the  north,  during  the  Trias-Jura,  it  is  scarcely  supposable  that 
the  thick  sediments  which  must  have  formed  should  have  disappeared  without  traces  which  would  have  been 
detected  before  now;  aud  while  ouly  an  elaborate  field  study  can  establish  the  facts,  it  seems  allowable  to  suggest 
the  probability  that  the  subsidence  of  the  Archaean,  which  took  place  at  the  close  of  the  Carboniferous  in  western 
Nevada,  did  not  extend  to  central  Arizona,  so  that  the  continental  area  of  the  Trias-Jura  embraced  eastern  Nevada, 
western  Utah,  and  most  of  Arizona,  excepting  the  northeastern  corner.  The  Pacific  coast  ol  that  time  followed  the 
meridian  of  117°  30'  (approximately)  to  the  neighborhood  of  Owen's  lake.  If  the  supposition  stated  above  is  correct, 
it  must  then  have  left  the  Palaeozoic  area  and  continued  in  a  southerly  or  southwesterly  direction.  It  appears  most 
probable,  on  the  whole,  that  it  passed  to  the  south  of  fort  Tejon  and  out  into  the  area  at  present  covered  by  the 
Pacific.  The  coast  in  San  Bernardino  county,  California,  has  no  doubt  slowly  changed  its  elevation  repeatedly,  but 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


47 


Professor  Whitney  states  that,  while  in  that  county  a  belt  of  10  or  12  miles  next  the  coast  is  occupied  by  Cretaceous 
and  Tertiary  strata,  the  region  back  of  this  is  composed  of  granite  and  highly  crystalline  rocks  of  the  geological 
age,  of  which  nothing  is  known,  (a)  Such  descriptions  of  San  Bernardino  county  as  have  been  published,  however, 
show  that  the  rocks  are  extremely  similar  to  the  Archsan  of  Arizona,  and  in  the  absence  of  definite  information 
it  may  be  assumed  that  they  are  identical.  If  so,  there  is  a  body  of  Archaean  reaching  from  San  Diego  to  Camp 
Verde,  a  distance  of  about  300  miles.  Its  northern  limit  is  not  far  from  Owen's  lake,  ami  its  southern  extension  is 
unknown.  If  the  shore  line  of  the  Pacific  ocean  in  the  Mesozoic  era  passed  westward  or  southwestward  from  near 
fort  Tejon  to  the  present  coast,  Jura-Trias  strata  probably  underlie  the  coast  ranges  in  that  neighborhood,  and  it  is 
possible  that  they  may  somewhere  be  exposed. 

It  is,  of  course,  wholly  impossible  to  assign  a  date  to  the  Archaean  ranges  of  Arizona,  the  more  so  that  the 
topographical  maps  of  the  area  are  very  inaccurate.  These  mountains  scarcely  appear  to  form  a  portion  of  the 
Basin  range  system,  but  they  may  have  been  raised  at  the  same  time,  for,  though  their  lithological  character  differs 
greatly  from  that  which  prevails  in  those  ranges,  the  trend  and  general  relations  of  the  Archaean  mountains 
certainly  do  not  diifer  more  from  those  of  the  Palaeozoic  ranges  of  Arizona  than  the  Mesozoic  Sierra  Nevada  from 
the  ranges  of  the  same  era  in  western  Nevada.  It  at  least  seems  more  likely  that  the  Archaean  ranges  date  from 
the  post-  Jurassic  upheaval  than  from  cither  of  the  three  other  important  uplifts  mentioned,  while  it  scarcely  seems 
possible  that  any  traces  of  a  pre-Palteozoic  mountain  formation  should  have  withstood  erosion  till  the  present  day 
unless  protected  by  overlying  rocks  of  later  age. 

Of  the  eruptive  rocks  of  Arizona  not  much  is  known.  Besides  granite,  there  are  enormous  quantities  of  true 
basalt  and  of  other  volcanic  rocks  which  have  not  yet  been  subjected  to  the  minute  examination  necessary  to  classify 
them  satisfactorily.  The  census  collection  contains  numerous  specimens  of  pre-Tertiary  eruptive  rocks,  quartz- 
porphyry,  diabase,  and  diorite.  If  the  analogy  of  Nevada  could  be  trusted,  these  rocks  would  be  regarded  as  Mesozoic, 
aud  as  probably  post- Jurassic.  They  appear  in  the  Palaeozoic  ranges,  not  merely  as  dikes,  but  as  lai\;e  masses, 
inclosing  veins,  and  their  extrusion  was  most  likely  a  concomitant  of  the  disturbance  to  which  the  formation  of  the 
ranges  is  due.  Though  only  an  examination  in  the  field  can  determine  the  age  of  those  mountains,  the  occurrence 
of  ttiese  eruptives  is  another  argument  for  referring  them  to  the  great  Mesozoic  upheaval. 

The  census  collection  of  the  Pacific  division  contains  only  a  single  syenite.  This  forms  the  hanging  wall  of 
the  Golden  Eagle  mine,  Globe  district,  Pinal  county,  Arizona  territory.  A  slide  shows  orthoelase,  a  little  plagioclase, 
hornblende,  mica^  and  scarcely  a  trace  of  quartz.  The  exploration  of  the  fortieth  parallel  encountered  but  one 
syenite.  This  was  found  in  the  Cluro  hills,  Cortez  range,  Nevada,  and  contains  much  more  quartz  than  that  from 
the  Golden  Eagle  mine.  The  latter,  however,  bears  a  strong  resemblance  to  the  granite  which  is  the  prevailing 
rock  in  the  Globe  district,  and  is  represented  in  the  census  collection  by  a  large  number  of  specimens.  The  Cluro 
Hills  syenite  is  also  scarcely  distinguishable  from  the  granite  of  the  same  region,  and  it  may  fairly  be  asked  whether 
both  are  not  to  be  considered  as  granites  containing  an  unusually  small  proportion  of  quartz.  As  is  well  known, 
almost  every  fresh  investigation  of  European  syenites  diminishes  the  number  of  occurrences  to  which  the  name  is 
•ousidered  applicable,  and  it  seems  not  unlikely  that  it  will  eventually  disappear  from  the  list  of  rocks. 

The  ore  deposits  of  Arizona  in  a  majority  of  cases  are  found  in  connection  with  massive  rocks.  Often  both 
walls  are  granite  or  some  later  eruptive;  in  many  cases  a  massive  rock  forms  one  wall  of  the  veins,  and  even  where 
limestone  or  shale  entirely  inclose  the  ore  it  is  known  in  some  cases  that  eruptive  rocks  occur  close  in  the 
neighborhood.  The  relations  of  the  mineral  belt  as  a  whole  to  the  southwestern  edge  of  the  area  of  post- 
Carboniferous  upheaval  have  already  been  sufficiently  commented  on. 

• 

AFAC1IK  COUNTY. 

In  the  northern  part  of  this  county  good  coal  seams  exist  in  the  Cretaceous,  but  at  present  they  are  little 
exploited  for  want  of  facilities  for  transportation.  At  the  southern  end  of  the  county,  where  it  adjoins  Pima, 
cupper  ores,  with  blende  and  pyrite,  occur  in  the  veins  associated  with  limestone  and  quartz»porpbyry.  There  are 
also  gold  placer  mines  in  the  same  neighborhood,  and  consequently  there  must  be  gold  quartz  veins,  though  none 

such  have  been  reported  by  the  experts. 

APACHE. 


WAI 

ItM. 

Character  of 

Foot. 

Hanging. 

deposit. 

COPPER  MOUNTAIN. 

Melaconite  and  azurito,  zincblende,  pjrite,  with  cal- 

l.KI.KXLEE GOLD  MOUNTAIN. 

careous  gangue. 

Probably  diorite           .  .  ... 

Placer. 

Quartz-porphyry. 

a  Auriferous  Gravel*,  \).  If. 


48 


PRECIOUS  METALS. 


MARICOPA  COUNTY. 

Maricopa  county  includes  a  portion  of  the  plateau  country,  and  extends  across  the  range  system  far  into  the 
Archteau  area.  The  principal  mining  district  in  this  county  is  the  Globe,  about  half  of  which,  however,  lies  in 
Final  county.  The  principal  ores  are  argentite  and  cupriferous  minerals,  associated  with  galena  and  zincblende. 
The  ordinary  gangue  mineral  is  quartz,  but  heavy  spar  also  occurs.  The  inclosing  rocks  are  usually  granite  or 
highly  metamorphosed  strata,  but  the  walls  of  the  Mexican  mine  appear  to  be  diabase.  This  district  is  nearly  on  the 
contact  between  the  Palaeozoic  and  the  Archaean. 

MAEICOPA. 

• 

[NOTH. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.] 


WAI 

<LB. 

Character  of 

Mine. 

Ore  and  gangue. 

Foot. 

Hanging. 

deposits. 

GLOBB. 

Argontite     erubescite,    and  chalcopyrite  ;    gangue 

Metamorphic  diorite  *  

Metamorphic  diorite  *  

Probably  vein. 

quartz  and  barite. 

Granite  ;  

Do. 

Diabase  

Diabase  -  

Do. 

zmc,  which  on  the  lower  levels  take  the  form  of 
sulphurets;  also  gold). 

Granite  

Granite  

Do. 

...do  

Do. 

arsenide  of  copper,  (also  silver  and  horn-silver). 

Mica-schist  

Mica-schist  

Probably  vein. 

*  Microscopically  examined. 


MOHAVE  COUNTY. 

Mohave  county  lies  in  the  northwestern  corner  of  Arizona.  The  best  known  district  is  the  Hualapai, 
containing  Mineral  Park,  which  lies  a  few  miles  to  the  west  of  the  Palaeozoic  area.  The  country  rock  of  the  Mohave 
county  mines  is  almost  exclusively  granitic,  but  a  gneissoid  structure  is  said  to  bo  apparent  in  many  cases.  The 
ore  occurs  in  veins  with  quartz  gangue,  and  consists  of  argeutite.,  stephanite,  ruby  silver,  freibergite,  etc., 
accompanied  by  galena,  zincblende,  and  copper  pyrite  and  mispickel. 

Near  the  croppings  these  ores  are  largely  converted  into  horn-silver  and  native  silver,  which  are  readily  worked ; 
but  at  some  distance  from  the  surface  most  of  them  become  very  base.  Many  disappointments  in  the  working  of 
Arizona  mines  have  been  due  not  to  the  exhaustion  of  the  ore,  but  to  the  fact  that  below  the  water-level  the  ores 
were  found  to  be  rebellious.  Such  ores  can  be  worked  at  a  profit  under  the  prevailing  economical  conditions  only 
when  very  rich. 

MOHAVE. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts. ) 


Mine 

WAI 

,L8. 

Character  of 

• 

Foot. 

Hangfcg. 

deposit. 

HUALAr-AI. 

Cerbat  

(Granite) 

(Granite) 

Vein 

Champion  

probably  of  chloride  of  silver. 

do 

do 

Do. 

Fail-field  ... 

.  quartz. 

Granite  * 

Granite* 

Do 

Indian  Boy  

Do 

Keystone  

((Inuiitc) 

(Granite) 

Do 

I/one  Star  

quartz  gangue. 
Rubv  silver  and  indeterminable  black  sulphuret  stains- 

Do. 

Pure  Metal  

quartz  gangue. 

(Granite) 

(Granite) 

'Do 

MAYNABD. 

American  Flag  

Vein 

Peabody  

and  copper  pyrites,  (freibergito,  native  silver,  and 
mispickel),  quartz  gaugue. 

do 

do 

Do 

Hackberry  

•    do 

do 

Do 

silver  ;  quartz  gaugue.) 

' 

Microscopically  examined. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  40 

Hualapai  district  i.->  very  large,  and  contains  a  number  of  mineral  neighborhoods.  At  Chloride  veins  occur  in 
granite  with  quart/  gaugue.  Xcar  thesurface  the  ore  minerals  are  carbonate  of  lead  and  silver  chloride.  Below  the 
water  level  these  are  replaced  by  galena  and  pyrite.  The  mines  mentioned  are  :  Schenectady,  Schuylkill,  Empire, 
Juno,  Silver  Hill,  Pinkeye,  Kanawha  Belle,  Oriental,  and  Porter.  Xear  Stockton  deposits  are  found  which  are 
similar  to  the  foregoing,  but  they  are  reported  as  containing  also  native  silver  and  ruby  silver,  as  well  as  ziucblende, 
chalcopyrite,  and  some  stibnite.  The  mines  mentioned  are:  Indian  Boy,  I.  X.  L.,  Tiger,  Ed.  Everett,  Cupel, 
Dolly  V.,  Pure  Metal,  Little  Chief,  Prince  Geo.,  and  Tigress.  At  Mineral  Park  native  silver  and  silver  chloride 
occur  near  the  croppings  of  the  veins  which  carry  a  quartz  gangue  and  are  inclosed  in  granite.  The  undecomposed 
minerals  are  argentite,  ruby  silver,  stephauite,  with  some  galena  and  zincblende,  iron  pyrite,  and  arsenical  pyrite. 
The  mines  mentioned  are:  Keystone,  Lone  Star,  Fairfield,  Quick  Relief,  Conner,  and  Metallic  Accident.  At 
'Cerbat  the  ore  thus  far  mined  carries  horn-silver  in  a  quartz  gangue,  with  some  native  gold  and  silyer,  complex 
sulpharseuides,  and  antimonides  and /incblende.  The  mines  mentioned  are :  Cerbat,  Black-and-Tan,  Suowflake, 
Mocking  Bird,  Sixty-Three,  Falstaff,  Fonteuoy,  Champion,  New  London,  Flora,  and  Paymaster. 

The  Maynard  district,  like  the  Hualapai,  shows  quartz  veins  in  granite  and  mineral  associations  similar  to  that 
last  mentioned.  The  mines  reported  are :  The  American  Flag,  Peabody,  Dean,  Antelope,  and  Mississippi. 

The  Cedar  Valley  district  is  also  in  a  granite  country.  The  ores  are  argentiferous  galena,  ruby  silver,  tetrahedrite, 
and,  near  the  croppings,  horn-silver,  accompanied  by  zincbleude,  pyrite,  and  quartz.  The  mines  mentioned  are: 
Silver  Queen,  Hibernia,  Hope, 'General  Lee,  Arnold,  Hilly  Eugle,  Eainbow,  Eugenie,  Bunker  Hill,  Congress, 
and  Gunsight. 

Owens  district  is  in  a  granite  country,  but  a  portion  of  the  rock  is  gneissoid.  The  ores  are  argentiferous  galena 
and  argentite,  with  decomposition  products  near  the  croppiugs  and  a  quartz  gangue.  The  mines  of  the  McCracken 
company  and  the  Signal  mine  are  the  chief  ones  of  the  district. 

PIMA  COKNTY. 

This  county  occupies  the  southern  end  of  the  territory,  and  crosses  the  mineral  belt.  It  contains  a  very  large 
number  of  districts,  the  most  famous  of  which  is  Tombstone.  Many  of  the  mines  in  this  district  are  in  limestone, 
and  carry  chiefly  argentiferous  lead  ores.  Manganese  minerals  (pyrolusite  and  wad)  sometimes  accompany  them, 
in  large  quantities.  There  are  also  veins  in  the  Tombstone  district  in  quartzite.  These  carry  cupriferous  minerals 
more  or  less  charged  with  silver  and  some  free  gold. 

From  mine  reports  and  papers  by  Professor  W.  P.  Blake  it  appears  that  the  ore  in  the  Tombstone  district 
occurs  in  Paleozoic  beds,  probably  of  Carboniferous  age,  which  have  a  prevailing  inclination  to  the  north  and 
east,  resting  on  a  granitic  base,  which  outcrops  some  distance  to  the  southwest.  These  beds  consist  of  a  tine- 
grained  qnart/ite,  called  by  him  novaculite,  about  140  feet  in  thickness,  underlaid  by  a  light-colored  dolomitic 
limestone  and  overlaid  by  a  blue-black  limestone  passing  into  shaly  beds.  The  principal  portion  of  the  ore  is 
found  at  the  horizon  of  this  blue-black  limestone.  The  sedimentary  formations  have  been  compressed  into  a  series 
of  sharp  folds  and  fissured  and  traversed  by  dikes  of  pre-Tertiary  eruptive  rock,  known  in  the  district  as  diorite. 
The  census  collection  from  Tombstone  contains  both  diorites  and  diabases.  The  general  direction  of  the  fissures  and 
dikes  lies  between  north  and  northeast.  The  ore  occurs  both  in  fissures  which  cross  the  strata  either  parallel  to 
or  in  direct  connection  with  the  dikes  and  in  bodies  branching  out  from  these  approximately  vertical  bodies  in  a 
more  horizontal  direction,  following  in  general  the  bedding  planes  of  the  formation,  whose  prevailing  dip  is  to  the 
northeast.  The  ore  is  most  abundant  and  richest  in  that  part  of  the  black  limestone  beds  which  are  contiguous  to 
the  quartzite,  and  the  vertical  fissures  generally  contract  and  become  less  rich  where  they  cross  the  quartzite  itself. 
Their  continuation  in  the  lower  limestone  beds  has  not  yet  been  much  explored.  In  the  origin  and  manner  of 
deposition  of  its  ore  bodies  the  district  would  seem  to  resemble  that  of  Chauarcillo  in  Chili. 

There  are  also  veins  in  the  granite,  or  associated  with  it.  near  Tombstone,  which  are  similar  to  the  other 
deposits  of  the  territory  found  in  this  rock.  The  group  of  districts,  including  the  Oro  Blanco,  Arivaca,  Harshaw, 
etc.,  just  north  of  the  Mexican  line,  seem  to  possess  much  the  same  character  as  Tombstone.  The  country  rock- 
is  granite,  limestone,  quartzite,  or  earlier  eruptive  rocks,  and  the  ores  are  galena  and  its  products  of  decomposition, 
ordinarily  accompanied  by  copper  minerals  and  charged  with  silver.  They  are  sometimes  auriferous.  In  the 
western  part  of  the  county  there  are  gold  and  copper  mines,  with  some  lead  ores.  These  are  sunk  on  veins  in 
granite,  which  carry,  besides  quartz,  tiuorite  and  heavy  spar  as  gangue  minerals. 
VOL  18 4 


50 


PRECIOUS  METALS. 


rniA. 

[NOTE. — Determinations  ill  parentheses  arc  jjiveu  c,n  (lie  itiithority  of  the  experts.] 


Mine. 

Ore  and  gaugue. 

WALLS. 

Character  of 
deposit. 

Foot.                                         Hanging. 

AlilVAl-A. 

Copprrstaius  and  black  sulplmrets  in  small  quant  ities, 
with  quartz  and  barite,  (also  chlorides  aiid  carbon- 
ates). 

The  ore  shows  blue  stains,  which  are  possibly  horn- 
sUver.  (free  gold  and  horn-fliiver),jailffue  quart  /.and 
Uroonite. 

(Fre<-  gold  and  horn-silver),  gangue  quart/-  and  limo- 
uite. 

Vein. 

Vein. 
Do. 

Pockets. 
Do. 

Vein. 

Do. 
Do. 

Vein 

Vein. 
Do. 

Do. 

"  Flat." 
Vein. 

Vein. 

Connected  poekets 

Connected  pockets. 
Do. 

Connected  pockets. 

Do. 
Do. 
Do. 
Do. 

Veto. 

Do. 
Do. 
Do. 

Probably  vein. 
Vein. 

Pocket*. 
Vein. 
Do. 
Do. 

Do. 
Pockets. 

Vein. 

1  Vein. 
Probably  vein. 

liOS  CAHICZAS. 

Shale    Shale  

• 

(Slate)  

IIAKSHAW. 

Quartzite. 
Limestone  

Ceiua.site  and  <uprif  rous  minerals,  (iciucblcnde,  g;i- 
Icna,  j'lid  antimon;al  niineiuls,  g:nii;ue  quart/,  and 
limestone). 

Limestone  

r;  mm  t«  * 

do 

HAUTFOI1I). 

Malachite,  (liom-pilver),  gangm.1  hem,  trite    Limestone  

Gal  na,  cerussitc,  rop;  cr  staiiiH.  ujin^iu-  quartz,  ilao-  ;  (Granite)  
rile,  and  huavy  s]mr. 

i 
Do. 

MITEB8. 

Atlanta  

do  

'i;ilt-n;i,    hoin-silvrr,  copper  stains,  ganj^ue  quartz, 
baiite,  and  ln.'ihaiite. 

Granite  

MULE  PASS. 

QUO  IILAXCO. 

Malachite,  (carbonates  with  copper  and  lead)  

Galena,  crrussile.  malachite  ;  possibly  stephauiteaud 
liorn-silvcr,  (jusirt/  unn^ue. 

Quartz  conglomerate  

Quart/  conglomerate  

Conglomerate  

(  i  ninite  *" 

Uttrrly  decomposed  
r,r:iiiit,n*  .. 

Galena,  fmbergit".  and  rlialcopyritc,  (carbonate  near 

SIM  lace),  ^.an^uc  quart/,  ir;ilc-.sparj. 

Galena,  pyi'ite,  :iud  chaloopyrile,  yan^ue  kaolinite    .. 
Galeiia  and  chalcopyrite,  <xangue  quartz  

OcrusHitu,  ^anguu  quartz,  liniouite    

Diorite  •  Diorite  *  

riMA. 

1 

Limestone  

SWISSUELM. 

3I.:i!.  moth  and  Whale  

do           

TOMH8TONK 

iiitl.  n;i,  cirti^-itr.  iiutiachite,  t-hn  -socolla,  and  proba- 
bly niiiut'titc,  (lioru-silver).  gangne  clay,  (quartz). 

Cernssite,  (horu-silver,  gangue  calcite)  
ilabu-hile,  (bom-silver),  gaugne,  quartz,  and  calcite.  , 

Probably  quartz-porphyry  .  .  |  

Metamorphic  *  
S.imlstone  

Solfatarically  -  decomposed 
eruptive  rock. 

Quartzite  *  
...do     

I.imnatono  
{  Sandstone)  

<  i  rand  Central  

Minute  specks  of  black  sulphurets,  (horn-silver  niid 
ceiussite),  gangue  quartz  and  liniuuitc. 

Horn-silver,    malachite,    and    chrysocolla,    (gangue 
qaartz  and  calcito). 

(Gold  and  horn-silver),  gaiigue  quartz  and  limonite... 
Anglcsitcand  ccrussite.fhorn-silverand  copper  stains)  . 

Cerussite  and  hom  silver,  (free  gold),  gangue  calcite, 
limouite,  (manganese  minerals). 

Corussito,  (horn-silver),  gangne   iron    oxide,  {quartz 
-    and  calcite). 

Cerussite  and  horn-silver,  (free  gold),  gangue  limo- 
uite, and  calcite,  (quartz). 

(Chlorides  and  carbonates),  gangue,  pyrolusite.  
Cerussite,-  (chloride  and  carbonate,  gangue  calcite)  .  .  . 
(Chloride  and  carbonate),  gangue,  wad,  (iron  oxide).. 

(Free  gold  and  trace  of   silver),  gangue,  ferruginous 
quartz. 

(Chlorides  and  carbonates),  gangue,  terruginousquartz, 

Cerussite,  (horn-silver  and  copper  carbonate),  gaugiu-, 
limonite,  and  fluorite,  (quartz  and  limestone). 

(Iloru-silver),  gangue,  limonite,  and  pyrolusite  

Galena  and  ceiu8site,(very  littlesilver),  gangue,  quart? 
and  limouite. 

Chalcopyrite,  bornite,  and  malachite,  ganguo  frag- 
ments of  rock. 

Quiivtzitc*  
....do  
.do    

Mamie  
Monitor  

Black  limestone  

Black  limestone  

Ke<l  Top  

•:tone\vall  

Limestone    
Diabase  
Limestone  

Granite 

Sulphuret  

Diabase  

Sunset  ... 

Ti'iua  

Toii£lmut  Extension  

(Porphyry  for  100  feet),  linns- 
stone  iu  part  siliceous. 

Limestone,  decomposed  dio 
rite,  (and  quartzite). 

Diabase*  
Limestone  

(  Porphyry  for  100  feet),  lime- 
stone in  part  siliceous. 

Limestone,  decomposed  dio- 
rite,  (and  quartzite}. 

Diabase*  
Limes  tone  

ToiighiiMt  and  Goodeuouph.. 
True  Blue  

TURQUOISE. 

Defiance  

Ajo  

*.  Microscopically  examined. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


51 


FINAL  COUNTY. 

Mcst  of  the  mines  of  this  county  are  found  in  the  northeastern  portion,  near  the  edge  of  the  Palaeozoic.  The 
ores  are  argeutite  and  the  sulphantimonide  minerals,  often  associated  with  lead  ores,  commonly  also  with  those 
of  copper,  and  sometimes  accompanied  by  zincblende.  The  gangue  minerals  are  quartz,  calcite,  occasionally 
manganese  compounds,  and  sometimes  (in  granite)  heavy  spar.  Limestone,  slate,  sandstone,  and  quartzite,  as  well 
as  granite,  diabase,  and  diorite  occur  as  wall  rocks.  Cupriferous  minerals  are  less  apt  to  be  associated  with 
limestones  than  with  other  metamorphic  rocks  or  granite  and  diabase.  The  famous  Silver  King  mine  is  in  the 
Pioneer  district  in  this  county,  and  its  great  yield  is  a  sufficient  refutation  of  the  statement  sometimes  made  that 
large  deposits  of  good  ores  do  not  occur  in  granite,  for  the  country  rock  of  this  mine  is  a  typical  granite,  though 
locally  called  syenite.  A  very  great  number  of  ore  minerals  occur  in  the  Silver  King,  the  specimens  showing  native 
silver,  stephanite,  freibergite,  chalcopyrite,  erubescite,  strorneyerite,  copper  carbonates,  galena,  and  zincblende.  The 
gangue  is  quartz  accompanied  by  barite.  Half  of  the  Globe  district  occurs  in  Final  county.  Its  characteristics 
have  already  been  mentioned  under  Maricopa. 

FINAL. 
[NOTE. — Del crmiuat lout)  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 

Ore  and  gangue. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

GLOBE. 

Galena,  limonite,  and  malachite;   quartz  and  pyrite 
gangue. 

(Carbonates,  some  lead,  and  a  little  arsenic),  gangue, 
psilomelane,  quartz,  limouite,  and  cblorite. 

Copper  stain*  and  specks-which  are  probably  stromey- 
eiite,  (chloride)  ;   gangue  quartz,  probably  manga- 
nese. 

(Sulphides   and  chlorides),  gangue  psilomelane  and 
quartz. 

Stromeverite,  gangue  kaolinized  rock  -  

Vein. 
Do. 
Do. 

Do. 
Do. 

Vein. 

Do. 
Do. 

Silver  Era 

PIONEER. 

Native    silver,   freibergite,    stephanite,    zincblende, 
chalcopyrite,  erubepcite,  malachite,  azurite,  galena, 
nnd  stromeyerite,  gangue  quartz  and  barite. 

(Gold  and  carbonates),  gangue  quartz,  probably  man- 
ganese minerals. 

Galena,  polybasite.miargy  rite.  pyrargyrite,  and  chalco- 
pyrite,   (stephanite,    argent  it  e,    and    zincbleude)  ; 
gangue  calcite  and  (quartz). 

Granite*  

Quartzite  

KI  Capitaii.. 

'.Microscopically  examined. 

YAVAPAI  COUNTY. 

The  mining  districts  of  this  county  are  chiefly  in  its  southwestern  portion,  near  the  edge  of  the  Palaeozoic 
;ii ca.  There  are  some  gold  quartz  veins  in  granite  and  granite-porphyry  in  this  county,  and  silver  veins  occur 
under  similar  conditions.  It  seems  not  improbable  that  the  relations  of  these  two  classes  of  veins  are  the  same  as 
in  Idaho,  but  this  cannot  be  asserted  without  further  information  than  is  now  available.  Most  of  the  deposits, 
however,  are  veins  in  metamorphic  rock  carrying  lead  and  copper  minerals  as  well  as  silver.  Heavy  spar  occurs 
as  a  gangue  in  the  Silver  Belt  mine,  gneiss  or  granite  forming  the  hanging  wall. 

YAVAPAI. 

[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot.                                         Margins. 

BIO  HUG. 

Silver  Belt 

Galena  and  cerassite,  (  oxides  and  chlorides),  gangue 
barite  and  calcite. 

Metamorphic  

Metamorphic  
Granite 

Vein: 
Vein. 
Vein. 

Vein. 
Chimneys. 

CIIEIIHV  CHEEK. 

HI  MBUG. 

Tip  Top 

Pyrargyrite.  zincblende,  and  pyrite,  (chlorides  on  the 
upper  levels),  gangue  quartz. 

(Carbonates  and    chlorides,    galena    and    antin  <u  y, 
gauguu  quartz,  iron  oxide,  and  calcit*'.) 

Galena,    rerussite,    and    copper    stains,   (chlorides), 
gangtie  (country  rock). 

l-KIK. 

Pack 

Slate  

Quartzite  

do 

do  

T1UKU. 

Ti«cr (julfiia.  /.ii.clili  nilr,  ::nd  pyritc  ;  gnngm'  quartz 


[  Granite : Vein. 


52 


PRECIOUS  METALS. 


YUMA  COUNTY 

Most  of  the  mines  of  this  county  are  near  the  Colorado  river.  They  are  sunk  on  quartz  veins  in  highly 
metamovphie  rocks  or  granite.  The  William  Penu  and  other  mines  in  the  Castle  Dome  district  are  associated  with 
a  greenstone,  which  proves  under  the  microscope  to  be  diorite.  The  ores  of  Yuma  county  are  chiefly  silver  ores, 
accompanied  by  lead  minerals.  Fluorspar  and  heavy  spar  are  found  ii:  many  of  the  veins  which  are  inclosed  in 
granite. 

YUMA. 
[NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.  1 


WALLS. 


Mine. 

CASTLE  DOME. 

Flora  Temple 


Ore  and  gangnc. 


Foot. 


(Argentiferous  galena  and  anglesite),  gangue,  (flu- 
orspar, calc-sp.ar,  quartz,  and  gypsum). 

Galena  Chief (Ore  same  as  above),  gangue,  fluorspar,  and  calcite.  -  - 

Norma '  Galena,  cerussite,  and   anglesite,   ganguo  fluorspar 

and  oalcito. 

1'ocaluintaa  Same  as  Norma 

William  IVnn do 


Hanging. 


Character 

deposit. 


•Gneif  s,  .-late,  mid  diorite*. .  I  Gneiss,  slate,  and  diorite* 


rriucesn '  Galena    and    c.emssite,  (argfiitite  and    hoin-silvor),     Granite  and  micaceous  slate, 

gangue,  cnlrile,  (ijimtz,  fluorspar,  unit  liarite).  '      capped  with  eonglomerate. 

lied  Cloud |  Cerussite,  anglesite,  and  hom-silvcr,  frangiie.  manga-     Granite 

nese  rainei-als.  iron  oxide,  quartz,  fluoriic.  barite. 

Hover I  Gangne,  calcite. 


Same  as  foot  wall 

Hornblende-andesite.* 


Vein. 


Vein. 


.  *  Mieroseopically  examined. 

IDAHO  TERRITORY. 

GENERAL  CHARACTER  OF  THE  TERRITORY. — Idaho  lies  in  the  northeastern  corner  of  the  Great  Basin,  directly 
southwest  of  the  Bitter  Hoot  mountains.  The  southern  portion  of  the  territory  resembles  the  regions  farther  south , 
its  southwestern  porl ion  forming  a  continuation  of  the  Nevada  sage-brush  deserts  and  the  southeastern  corner 
being  the  northern  end  of  the  sandy  and  alkaline  deserts  of  western  Utah.  The  upper  branches  of  the  Snake 
river,  the  sources  of  which  are  in  the  Yellowstone  park  and  the  Teuton  range,  just  east  of  the  Idaho  line,  unite 
about  f>0  miles  west  of  that  boundary.  For  a  shoit  distance  from  the  junction  the  course  of  the  river  is  nearly 
south,  but  it  bends  gradually  westward  and  northward,  reaching  the  Oregon  line  on  a  northwest  course.  The  area 
south  of  the  Snake  river  is  about  one-fourth  of  the  entire  territory.  The  valley  of  the  Snake  is  a  plain  from  50 
to  1(10  miles  in  width,  which  is  occupied  by  a  vast  sheet  of  recent  basalt  from  the  Wyoming  line  to  Owyhee  county. 
Immediately  to  the  north  of  this  plain,  which  has  an  elevation  of  a  little  over  4,000  feet,  the  character  of  the  country 
changes  abruptly,  and  most  of  the  rest  of  the  territory  is  extremely  mountainous,  many  of  the  suirimits  rising  to 
between  10,000  and  12,000  feet  above  sea-level.  The  climate  changes  with  the  topography.  Central  and  northern 
Idaho  are  east  of  Oregon  and  Washington  territory,  to  the  coasts  of  which  the  trade-winds  of  the  Pacific  bring  an 
enormous  amount  of  rain.  The  coast  is,  indeed,  separated  from  the  northern  portion  of  the  Great  Basin  by  the 
Cascade  range,  but  this  is  much  lower  and  much  less  continuous  than  the  Sierra  Nevada  to  the  south.  The 
westerly  winds  thus  bring  a  greater  amount  of  moisture  to  northern  Idaho  than  to  Nevada,  while,  the  lofty  peaks 
of  the  northern  area  promote  its  precipitation.  To  the.  north  of  the  Snake  River  region  Idaho  is  consequently  well 
watered  and  well  wooded,  conditions  of  the  utmost  importance  to  profitable  mining.  On  the  other  hand,  the  winters 
are  long  and  severe,  and  lines  of  communication  are  extremely  circuitous. 

Except  in  the  eastern  counties,  no  portion  of  Idaho  has  been  submitted  to  systematic  geographical  or  geological 
survey,  and  the  maps  of  the  territory  are  very  inaccurate.  The  geologic.)  1  information  furnished  by  the  census 
examination  is  necessarily  fragmentary,  presenting  only  data  from  a  large  number  of  mining  localities,  and  but  little 
assistance  can  be  derived  from  any  local  publications  with  which  I  am  acquainted.  The  following  paragraphs, 
therefore,  contain  only  a  very  rude  outline  of  the  geological  conditions  of  the  mining  regions  of  Idaho. 

A  very  large  giauite  area  occupies  a  portion  of  southwestern  Idaho.  It  appears  to  be  oval  in  shape,  its  longer 
diameter  extending  from  a  few  miles  south  of  Yankee  fork  nearly  to  the  South  Mountain  district,  while  its  shinier 
diameter  reaches  from  the  common  boundary  of  Washington  and  Boise  counties  in  a  southeastern  direction  to  the 
Wood  River  country.  Its  total  area  is  probably  about  12,000  square  miles.  Not  all  of  the  country  within  this  oval 
area  shows  granite  on  the  surface,  for  Ada  county  is  largely  alluvium,  and  Palaeozoic  limestones  are  reported  as 
occupying  much  of  the  more  northern  portions;  but  the  extremely  frequent  occurrence  of  granite,  for  the  most  part 
of  a  single  type,  appears  to  justify  the  supposition  that  the  body  is  continuous  under  the  later  formations. 

The  granite  from  the  Idlewild  mine,  Carson  district  (Silver  City),  Owyhee  county,  i  <  a  soft  gray  rock  with  rather 
well  developed  crystals  of  white  mica,  cleavage  flakes  of  which  give  the  biaxial  interference,  figure  of  muscovito. 
Slides  show  undei  the  microscope  that  llu-  constituents  are  orthoclase,  oligoclase.  quartz,  and  mica,  with  a  little 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  53 

apatite  and  magnetite.  The  quart/,  is  extremely  full  of  fluid  inclusions,  many  of  them  containing  moving  bubbles. 
The  sti  iicturo  is  the  ordinary  one  of  granite ;  indeed,  the  rock  is  quite  typical.  In  the  same  district  occur  excellent 
quart/  porphyries,  slides  of  which  show  dihexahedral  quartz  crystals,  with  the  characteristic  association  of  glass 
and  fluid  inclusions.  The  association  of  these  two  rocks  suggests  a  similar  origin,  or,  in  other  words,  that  the  granite 
may  be  eruptive,  but  of  course  proves  nothing.  On  the  other  hand,  there  is  no  known  evidence  tending  to  show  ;t 
derivation  of  the  granite  from  sedimentary  rocks.  The  granite  from  the  Sub  Rosa  mine,  in  the  Boise  basin,  is  in 
most  respects  similar  to  that  from  Carson  district,  though  about  80  miles  distant  from  it,  but  contains  biotite  in 
addition  to  the  muscovite.  In  several  localities  in  the  territory  the  granite  is  extremely  coarse-grained,  and  has  even 
furnished  marketable  mica  sheets. 

The  granite  has  been  profoundly  disturbed  by  eruptive  action,  aud  probably  at  a  comparatively  recent  date. 
The  evidence  of  this  is  manifold.  Dikes  of  eruptive  rock,  among  which  the  principal  one  appears  to  be  basalt,  (a) 
are  common  in  the  granite,  and  as  basalt  appears  everywhere  to  be  the  youngest  of  the  lavas  this  would  indicate 
comparatively  recent  action.  Hot  springs,  too,  are  thickly  distributed  through  the  granite  area,  in  many  cases 
issuing  directly  from  the  granite,  though  usually  within  a  mile  or  two  of  known  occurrences  of  volcanic  rocks. 
This  is  most  naturally  accounted  for  by  supposing  that  there  are  still  remnants  of  volcanic  heat  at  great 
depths  below  the  surface.  A  further  and  most  interesting  point  bearing  upon  the  structural  geology  of  the  region 
and  the  age  of  the  disturbances  is  the  fact  that  the  very  numerous  veins  found  in  the  granite  usually  strike  in  the 
direction  of  the  ranges  on  the  flanks  of  which  they  occur.  The  fissures  which  these  veins  occupy  must  have  been 
formed  by  an  upheaval  such  as  would  produce  these  ranges,  and  it  seems  necessarily  to  follow  that  the  mountains 
are  substantially  a  result  of  upheaval,  and  not  of  erosion.  ThFs  upheaval,  too,  must  be  comparatively  recent  in  a 
geological  sense,  say  as  late  as  the  Tertiary,  since  otherwise  the  results  of  upheaval  would  have  been  obscured  by 
subsequent  erosion.  The  occurrence  of  the  immense  lava  fields  of  the  Snake  River  valley  immediately  adjoining 
the  granite  area  suggests  that  the  dynamical  disturbances  and  the  thermal  action  manifested  in  the  granite  may  be 
a  portion  of  the  same  series  of  phenomena  to  which  the  Snake  river  eruptions  are  due.  The  age  of  the  veins 
themselves  is  quite  another  matter.  The  facts  mentioned  indicate  a  possibility  that  the  ores  have  been  deposited 
alter  the  upheaval  which  determined  the  present  topographical  character  of  the  country ;  it  may  be  through  the 
agency  of  the  solfataric  action  (b)  accompanying  the  basalt  eruption.  Indeed,  the  numerous  hot  springs  of  the 
granite  area  are  in  many  cases  highly  charged  with  alkalies  aud  sulphhydric  acid;  in  short,  they  are  solfataras. 
They  often  occur  in  the  immediate  neighborhood  of  the  mines,  one  of  the  mining  districts  in  the  Wood  River  country 
even  bearing  the  name  of  the  Hot  Springs  district.  In  a  mineral  region  solfataras,  active  or  extinct,  are  usually 
associated  with  ore  deposits,  which  are  commonly  ascribed  to  their  action,  and  it  is  difficult  to  see  lu>w  the  period  of 
solfataric  activity  now  drawing  to  a  close  can  have  failed  to  give  rise  to  metalliferous  concentrations  in  Idaho. 

On  the  other  hand,  the  structure  of  the  conulry  is  not  incompatible  with  the  supposition  that  the  veins  are  far 
older  than  the  basalt  and  a  concomitant  of  a  former  disturbance  of  the  granite.  Fissures  in  the  earth's  crust,  once 
formed,  seem  never  to  heal,  aud  faults  have  occurred  at  the  present  day  on  surfaces  upon  which  movements  are 
known  to  have  taken  place  in  the  Palaeozoic  era.  The  recent  upheavals  may  merely  have  followed  old  lines  of 
movement  which  had  been  marked  by  veins  long  before  the  present  mountains  rose.  An  indication  tending  to 
such  a  view  is  the  fact  that  some  veins  are  faulted,  though  this  is  not  the  rule,  while  slickeusides,  showing  relat:'~e 
motion  of  the  walls  of  the  veins  subsequent  to  the  deposition  of  ore,  are  very  abundant.  While  known  movements 
of  a  more  recent  date  than  the  ore  deposits  are  thus  shown,  the  extent  of  these  movements  usually  appears  to  be 
small.  Much  the  strongest  evidence  of  older  veins  is  furnished  by  the  placers  of  Boise  basin  and  the  canon  of 
Moore's  creek,  a  little  below  and  south  of  the  basin.  There  is,  of  course,  every  reason  to  suppose  that  auriferous 
gravels  are  accumulations  from  the  croppiugs  of  veins.  They  do  not  represent  the  whole  material  eroded  from  a 
country,  but  only  the  heavier  portion  which  the  streams  have  been  unable  to  carry  to  great  distances.  The  gravels 
of  Boise  basin  are  estimated  to  cover  .">(»  square  miles  to  an  average  depth  of  about  12  feet.  This  large  mass 
represents  not  merely  a  very  extensive  erosion  of  the  upper  country,  but  streams  of  a  size  inconsistent  with  the 
present  rainfall  of  the  territory.  It  does  not  follow,  however,  that  the  general  character  of  the  topography  of  the 
country  must  have  been  altered  by  this  erosion  to  such  an  extent  as  to  obscure  the  relation  of  the  strike  of  the 
veins  ro  the  trend  of  the  ranges.  Not  only  were  these  gravels  deposited  when  the  climate  was  much  inoister,  but 
they  date  from  a  time  prior  to  some  of  the  basalt  eruptions,  for  in  Moore's  creek,  the  outlet  of  the  Boise  basin,  the 
grave],  which  is  continuous  with  the  main  deposit,  is  covered  by  a  basalt  cap  which  can  scarcely  be  younger  than 
the  Snake  River  bed. 

In  the  light  of  the  present  knowledge  of  the  country,  it  seems  on  the  whole  most  probable  that  the  greater  part 
of  the  quartz  veins  of  this  region  are  of  Cretaceous  or  possibly  Tertiary  age,  but  it  is  by  no  means  unlikely  that  a 
part  of  them  are  subsequent  to  the  basalt,  and  thus  are  of  very  recent  date.  Should  this  be  established  by  future 
investigations,  it  would  afford  a  remarkable  instance  of  the  repetition  of  certain  chemical  and  physical  conditions 
at  considerable  intervals  in  geological  history. 

n  As  tilt'  enrjitiv-  rocks  ;irc  not  immeiliiitely  .-tssoehited  with  the  ore  deposits  in  any  of  the  mines  visited,  specimens  <•('  this  l>:jsa!t 
were  not  collected. 

b  See  note  to  page-  ti. 


54  PRECIOUS  METALS. 

A  very  large  portion  of  the  mines  in  Idaho  are  within  the  granite  district,  and  are  sunk  upon  veins  between 
granite  walls.  These  veins  are  very  similar  to  those  in  the  other  granitic  mining  districts  of  the  Great  Basin. 
They  are  numerous  and  rich,  but  narrow,  being  seldom  above  3  feet  in  thickness,  though  there  are  a  few  wide 
veins,  as,  for  example,  the  Atlanta,  Middle  Boise  district,  Alturas  county,  which  is  from  50  to  75  feet  across.  The 
gangue  of  the  veins  in  the  granite  area  is  quartz,  accompanied  by  more  or  less  decomposed  granite  as  horse  matter. 
The  ores  carry  both  gold  and  silver  in  very  varying  proportions.  The  gold  is  either  free  or  is  mechanically  entangled 
in  pyrite,  mispickel,  or  zincblende,  while  the  silver  appears  near  the  surface  as  chloride,  ;  ml  at  lower  levels  as 
sulphide,  stephanite,  tetrahedrite,  or  as  ruby  silver.  Zincblende  appears  occasionally,  and  galena  still  more  rarely. 
In  some  veins  gold  greatly  predominates,  in  others  silver;  yet  the  association  of  minerals  is  the  same  in  both  classes, 
the  relative  quantities  only  of  the  two  precious  metals  varying.  There  is  nothing  to  show  that  the  two  classes  of 
veins  are  of  different  origin  or  age;  on  the  contrary,  every  gradation  between  the  two  extremes  occurs,  and 
sometimes  both  are  represented  in  the  same  vein.  On  the  Atlanta  lode  the  Buffalo  and  Monarch  mines  produce 
about  twice  as  much  silver  as  gold,  while  in  the  Yuba  tunnel,  more  than  a  mile  distant  from  the  others,  but  on  the 
same  lode,  the  value  of  the  ore  is  almost  wholly  in  gold. 

From  a  geological  point  of  view  there  is  little  to  note  concerning  the  variations  of  the  ore  deposits  of  the 
granitic  area  without  going  into  more  detail  than  this  chapter  is  designed  to  record.  On  the  contrary,  the  most 
striking  point  connected  with  this  area  is  the  great  similarity  from  one  end  to  the  other  of  the  inclosing  rock  and 
.the  included  deposits.  As  soon  as  the  water-line  is  passed  suites  of  specimens  from  the  various  mines  are  almost 
indistinguishable,  except  in  point  of  richness.  In  prospecting  for  these  veins  it  would  be  well  to  observe  not  only 
the  float,  the  character  of  the  croppings.  and  the  like,  but  also  evidences  of  disturbance,  and  particularly 
decomposition  of  the  country  rock,  for  both  of  these  phenomena  are  likely,  though  not  certain,  to  accompany  the 
presence  of  ore. 

The  uniformity  in  character  of  the  veins  throughout  the  granite  area  of  Idaho,  in  spite  of  a  possible  difference 
in  age  and  their  dissimilarity  to  those  characteristic  of  other  formations,  is  highly  suggestive  of  the  nature  of  their 
origin.  It  is  almost  certain  that  the  ores  of  veins  are  precipitated  from  solutions,  and  that  these  solutions  acquire 
their  valuable  contents  either  at  great  depths  and  from  unknown  sources,  or  from  the  rock  masses  adjoining  the 
place  of  deposition.  The  latter  supposition,  which  is  known  as  the  lateral  secretion  theory,  has  been  gaining 
ground  of  late  years,  and  it  has  been  proved  in  many  cases  to  satisfy  all  the  known  facts.  Of  granite  in  particular 
Professor  F.  Sandberger  has  shown  that  the  mica  frequently  carries  various  heavy  metals,  and  he  has  pointed  out 
an  exceedingly  probable  series  of  reactions  by  which  these  metals  may  have  been  concentrated  in  veins.  In  the 
granite  of  Carson  district,  Owyhee  county,  Mr.  A.  Simuudi  has  detected  gold  (usually  amounting  to  at  least  L'5 
cents  per  ton\,  besides  silver,  even  at  long  distances  from  any  known  deposit  of  ore.  In  view  of  Sandberger's 
investigations,  it  is  improbable  that  this  content  is  due  to  impregnation  from  veins. 

If  it  be  supposed  that  the  Idaho  veins  are  due  to  metalliferous  solutions  rising  from  great  depths,  it  would  bo 
necessary  to  assume  that  the  granite  has  had  a  chemical  influence  on  the  precipitation;  for  if  this  were  due  merely 
to  reduction  of  temperature  and  pressure,  the  differences  between  the  deposits  in  granite  and  those  in  the  other 
rocks  of  the  territory  would  be  inexplicable.  But  the  Idaho  granite  appears  to  be  Archaean,  and  the  lower  surface 
of  the  Archa3an  has  never  been  reached  in  any  part  of  the  world.  Whatever  may  underlie  it,  it  is  certainly 
enormously  deep.  It  would  therefore  be  also  necessary  to  assume  that  the  granite  exerted  little  or  no  precipitating 
influence  at  great  depths  and  pressures,  but  only  within  a  certain,  no  doubt  large,  distance  from  the  surface;  for 
were  the  precipitating  action  vigorous  toward  the  lower  portion  of  the  granite  the  solutions  would,  for  the  most 
part,  be  robbed  of  their  metallic  contents  at  a  depth  of  miles.  If  this  were  the  case,  ore  veins,  if  reached  at  all, 
would  grow  richer  and  stronger  as  lower  levels  were  attained.  If  any  rule  can  be  established  in  regard  to  the 
relations  between  richness  and  depth,  it  is  rather  that  veins  grow  less  rich  and  strong,  though  strong  veins, 
probably  as  a  rule,  continue  metalliferous  to  a  greater  depth  than  mining  can  ever  be  carried  ;  but  the  cases  in 
which  veins  grow  better  in  proportion  to  the  depth  reached  are  certainly  very  exceptional. 

On  the  other  hand,  so  far  as  the  facts  concerning  the  veins  in  granite  in  Idaho  are  known,  the  supposition  that 
they  are  the  result  of  a  leaching  of  the  granite  itself,  probably  by  heated  waters,  appears  simple,  satisfactory,  and 
sufficient.  It  would  account  for  the  difference  between  the  veins  in  granite  and  those  in  other  rocks  by  the 
difference  in  the  rocks  themselves,  and  place  the  source  of  the  ores  in  the  neighborhood  of  their  present  position. 
Whether  any  actual  particle  of  ore  originally  formed  a  constituent  of  the  granite  on  the  same  level  or  a  few 
hundred  feet  below,  or  even  above,  no  one  would  of  course  venture  to  assert.  The  hypothesis  is  merely  that  the 
rock  in  the  neighborhood  of  the  veins  has  furnished  their  contents. 

Interesting  and  in  part  extremely  important  oie  deposits  have  been  discovered  in  the  sedimentary  rocks 
adjoining  the  granite  area,  and,  indeed,  on  all  sides  of  it.  It  has  been  asserted  that  a  portion  of  these  deposits  form 
a  continuous  mineral  belt.  So  broad  a  statement  can  hardly  be  indorsed,  but  there  is  sufficient  evidence  to  warrant 
the  assertion  that  the  zone  of  country  immediately  surrounding  the  granite  is  well  worth  prospecting  with  unusual 
care,  and  that  valuable  smelting  ores  are  not  unlikely  to  be  met  with  at  almost  any  part  of  this  zone  at  or  near  the 
granite  contact. 


GEOLOGICAL  SKKTCH  OF  THE  PACIFIC  DIVISION.  55 

Tin-  most  southerly  of  Iliis  class  of  deposits  are  those  of  the  South  Mountain  and  Flint  districts,  in  Owyhee 
county,  near  the  Oregon  line.  The  country  rock  is  chiefly  limestone,  and  the  ore  argentiferous  galena.  No  work  was 
done  in  these  districts  during  the  census  year  or  for  some  time  before,  not,  it  is  stated,  on  account  of  lack  of  ore,  hut 
in  consequence  of  financial  embarrassments  arising  from  the  failure  of  the  Bank  of  California  in  San  Francisco  in 
1875.  To  the  northwest  of  the  granite  lies  the  Heath  district,  in  which  rich  galena,  high-grade  copper  ores,  iron, 
and  lignite  are  reported.  No  description  of  the  country  rock  has  been  published,  and  as  the  district  was  idle  during 
the  census  year  the  census  examination  did  not  include  a  visit  to  it;  but  the  association  of  minerals  leaves  little 
doubt  that  the  area  is  sedimentary.  In  the  Yankee  Fork  district,  north  of  the  granite,  the  country  appears  to 
consist  of  gneiss  (a)  and  eruptive  rocks,  while  the  ores  show  gold  and  silver,  but  seem  to  carry  more  copper  than 
in  the  granite  district.  The  important  Custer  mine  is  in  this  locality.  In  the  Bay  Horse  district  slates  are 
accompanied  both  by  milling  and  smelting  ores,  lead  and  copper  being  often  prominent  constituents.  Both  this 
and  the  preceding  district  were  visited  by  Mr.  Williams  in  the  depth  of  winter,  when  work  on  almost  all  the 
mines  was  stopped,  and  it  was  impossible  to  obtain  entirely  satisfactory  suites  of  specimens. 

The  Wood  River  country  lies  southeast  of  the  granite  area.  Limestone,  slate,  and  granite  are  the  prevailing- 
rocks,  and  argentiferous  galena  (or  its  products  of  decomposition),  often  extremely  rich,  is  the  chief  ore.  As  is  so 
usually  the  case  with  galena,  the  ore  bodies  are  irregularly  distributed  in  limestone,  but  the  true  meaning  of  this 
association  has  never  been  fully  explained.  Mr.  Emmons,  in  discussing  the  Leadville  deposits,  regards  the  galena 
as  precipitated  by  substitution  for  the  limestone,  but  no  one  as  yet  has  indicated  the  probable  chemical  reactions 
involved.  Milling  ores  also  occur  in  the  Wood  River  country  in  the  granite  and  slate.  This  region  was  opened  up 
during  the  census  year, but  has  since  acquired  great  importance.  The  geographical  distribution  seems  to  indicate  that 
a  relation  exists  between  these  lead-bearing  districts  and  the  granitic  area  about  which  they  lie.  It  is  altogether 
probable  that  the  ore  was  deposited  throughout  the  whole  region  at  the  same  time  or  times,  and  that  the 
differences™  the  character  of  the  ore  are  attributable  to  the  different  chemical  and  physical  characters  of  the  rocks. 
Were  the  galena  deposits  all  on  one  side  of  the  granite  it  might  well  be  maintained  that  they  were  wholly 
independent  of  the  gold-quartz  veins  in  the  granite,  but  any  hypothesis  which  will  account  for  them  independently 
in  their  actual  distribution  appears  extremely  artificial. 

1  :«'sides  the  deposits  wluch  have  been  mentioned,  there  are  also  veins  carrying  precious  metals  in  Warren's 
ramp,  in  the  northern  part  of  Idaho  county.  The  ores  from  this  camp  are  quartzose,  carrying  free  gold  and  ores 
of  silver.  The  association  much  resembles  that  met  in  the  mines  of  the  great  granite  area,  and  the  country  rock 
i ;  also  reported  by  Mr.  Wolters  as  granite.  Gold  mines  also  occur  at  Iowa  bar,  in  the  extreme  eastern  portion  of  the 
territory.  Limestone  and  "porphyry"  are  said  to  be  the  accompanying  rocks.  Lignite  has  been  found  in  various 
portions  of  Idaho,  for  example,  in  the  valley  of  Boise  river  and  on  Reynold's  creek,  in  Owyhee  and  Oueida  counties, 
etc.,  but  no  commercially  valuable  deposits  have  as  yet  been  discovered.  Sulphur  occurs  in  connection  with  hot 
springs  in  Bear  Lake  county,  and  deposits  of  alkalies  exist  in  the  same  portion  of  the  territory.  Considerable 
quantities  of  float  cinnabar  have  been  found  in  Stanley  basin,  at  the  eastern  extremity  of  Bois6  county,  and  along 
t  he  Salmon  river  between  the  month  of  Yankee  fork  and  the  town  of  Sawtooth,  but  not  in  place.  Cinnabar  is  usually 
associated  with  Cretaceous  rocks  on  the  Pacific  coast,  and  this  fact  might  be  of  use  in  the  search  for  the  ore  if  the 
horizons  of  the  neighborhood  had  been  identified.  Tinstone  has  been  found  as  wash  in  the  bed  of  the  Jordan  river, 
Owyhee  county.  This  is  one  of  the  few  points  at  which  tifistone  has  been  encountered  in  the  far  west,  Temescal, 
San  Bernardino  county,  California,  and  Deer  Lodge  county,  Montana,  being  the  principal  other  localities. 

The  auriferous  gravels  of  Idaho  are  of  great  volume  and  extent.  Though  of  much  less  importance  than  those 
of  California,  they  have  been  more  productive  than  those  of  any  other  state  or  territory  except  Montana,  and  have 
probably  yielded  something  like  thirty  million  dollars'  worth  of  gold. 

Three  distinct  classes  of  auriferous  gravels  may  be  recognized  in  Idaho.  The  bars  of  the  Snake  river  are 
auriferous,  but  the  gold  is  in  an  extreme  state  of  division,  and  can  be  recovered  at  a  profit  only  in  exceptional 
cases.  Many  rich  but  small  placers  occur  along  the  banks  of  the  Salmon  and  of  the  other  rivers  of  Idaho,  and 
were  either  deposited  by  the  present  streams  during  freshets,  or  left  by  a  comparatively  slight  shifting  of  the 
channels.  Small  placers  have  usually  been  found  near  the  croppings  of  gold  veins,  which  have  undoubtedly 
furnished  the  auriferous  gravel,  and  a  large  part  of  the  veins,  as  in  California,  have  been  discovered  by  tracing 
these  gravels  to  their  sources.  Most  of  the  richest  of  the  small  placers  have  probably  been  worked  out ;  at  least 
few  new  ones  of  remarkable  value  have  been  discovered  for  many  years  ;  but  enough  is  left  to  furnish  occupation 
to  a  considerable  population.  The  deep  gravels  of  Boise  basin  are  of  a  different  character.  The  basin  is  surrounded 
except  at  one  point  by  mountains,  and  receives  no  drainage  from  beyond  its  own  limits;  yet  it  is  estimated  to 
contain  tome  125,000,000  cubic  yards  of  auriferous  gravel,  and  some  of  it  has  a  depth,  it  is  asserted,  of  no  less  than 
-'50  feet.  While  there  is  evidence  of  a  channel  in  a  northeastern  and  southwestern  direction,  the  gravels  spread 
over  nearly  the  whole  basin,  and  occur  even  on  the  tops  of  considerable  hills.  The  gravels  extend  several  miles 
down  Moore's  creek,  the  outlet  of  the  basin,  and  are  here,  in  part,  covered  by  a  heavy  basalt  cap.  The  pay-dirt  is 

a  A  slide  of  the  country  rock  of  the  Charles  Dickens  mine  shows  a  structure  usual  in  highly  metauiorphic  rocks,  corresponding  to 
its  microscopical  appearance,  lint,  the  constituents  are  so  thoroughly  decomposed  that  little  more  can  be  said  of  it. 


56  .  PRECIOUS  METALS. 

commonly  near  the  bed-rock  of  these  beds,  as  is  usual  elsewhere.  Large  bowlders  are  1'requeut,  as  aie  also  fossil- 
tree  stems,  which  are  so  characteristic  of  the  auriferous  gravels  of  California.  The  Boise  basin  deposits  are  not 
worked  out,  though  their  yield  has  decreased  during  the  last  few  years,  owing,  it  is  said,  rather  to  high  wages  and 
lack  of  water  than  to  dearth  of  good  gravel.  In  the  earlier  days  of  mining  in  Bois6  basin  many  extremely  rich  bars 
were  found,  which  were  undoubtedly  concentrations  from  the  older  gravels  by  modern  streams.  Pew,  if  any,  of 
these  rich  spots  can  have  escaped  the  eager  search  which  has  been  made  for  them.  It  would  be  impossible  to 
account  for  the  presence  of  the  gravels  of  the  Bois6  basin  at  the  head  of  a  system  of  drainage  without  a  special 
examination  undertaken  for  the  purpose,  but  it  may  be  considered  certain  that  a  great  river  once  flowed  through  the 
basin  and  transported  the  gravel.  Some  secular  or  paroxysmal  action,  not  improbably  a  concomitant  of  the  basalt 
eruption,  must  have  modified  the  topography  in  such  a  way  as  to  deflect  this  river,  but  the  character  of  the  change 
in  the  drainage  is  unknown.  The  Bois6  basin  gravels  were  probably  contemporaneous  with  those  of  California  ; 
for  the  present  rainfall,  as  has  already  been  pointed  out,  is  insufficient  to  account  for  them,  and  it  is  not  probable 
that  greatly  increased  precipitation  can  have  prevailed  in  either  of  two  districts  so  similarly  situated  as  California 
and  Idaho  without  its  being  shared  by  the  other.  The  fossil  plants  also  seem  to  be  the  same  or  extremely  similar, 
as  are  also  the  relations  to  the  basalt. 

The  following  sections  of  gravels  are  selected  out  of  a  considerable  number  to  illustrate  their  occurrence. 
The  third  of  these  is  noteworthy  as  an  exception  to  the  ordinary  rale  that  the  pay-dirt  lies  near  the  bed-rock. 

CREPISCULLA  HYDBAUL1C  MINK. 
MOOKE'S  CREEK  DISTRICT,  BOISE  COUNTY,  IDAHO  (SECTION  IN  NORTH  WORKINGS). 


Brown  soil 

1 1      Uniform  low-grade  gravel  of  median)  size 

III  I  Bowlder  stratum  (quartz  and  granite) 

IV  |  Bed-rock  granite ;  hard  when  first  uncovered,  slacking  rapidly  on  exposure. 

' 


C  None  absolutely  barren,  but  tbe  bulk 

47  feet.         >  Maximum.  70  feet <    of  the  gold  is  thought  to  come  from 

]  O-'O  feet  '        the  lowest  quarter  of  the  bank. 


The  bank  shows  a  fine  section  across  the  river  bed  550  feet  wide,  which  is  now  left  at  the  summit  of  a  low  hill.     Ibis  part  of  the  claim  is  from  360  to  450  feet 
higher  than  the  south  workings. 

R.  VV.  SPENCER'S  HYDRAULIC  MINK. 
BOSTON,  BOISE  COUNTY,  IDAHO. 


II 


m 


Loam,  with  some  small  quartz  bowlders 3  feet.    >  Maximum,  10  feet ;  average, 

Quartz,  gravel,  and  clay,  with  small  bowlders  not  over  9  inches  in  diameter,  I  3  feet,    t 
chiefly  granite. 

Bed-rock ;  soft,  decomposed  granite. 


(  Grass-root  gold.     Color  throughout 
(    deposit.     Best  pay  on  bed-rock. 


NOBLE,  LOWER  &  MANN  HYDRAULIC  MINE. 
MOORE'S  CREEK  DISTRICT,  BOISE  COUNTY,  IDAHO. 


I 

II 
III 
IV 


Soil..... t 2  feet,  1 

Quartz,  gravel,  and  clay . .  I  2-6  " 

Rotten  bowlders  of  quartz  and  granite,  9  inches  to  4  feet  in  diameter I  10 

Bed-rock  granite;    very  rough,  hard  when  first  uncovered,  but  slacking 
rapidly  on  exposure. 


p  (•„  *  i  Maximum,     30     feet ;  \  Tjpper  3  feet  from  surfaeois  the  pay- 

f  average  where  work-  \\   ing  portion. 
-15  feet,       )    inS.  13  feet- 


River  bed  300  feet  wide  and  2,000  feet  long  on  claim.  The  bowlder  stratum,  III,  is  too  poor  to  pay  for  wwVing  by  itself,  but  all  has  to  lie  piped  off  to  obtain 
grade  for  race — one-fifth  good  pay  and  lower  four-fifths  low  grade. 

SUMMARY  BY  COUNTIES. 

ADA  COUNTY. — There  is  very  little  mining  in  Ada  county,  the  principal  industry  being  agriculture.  The 
occurrence  of  galena  not  far  from  the  granite  area  of  the  adjoining  counties,  however,  is  an  interesting  fact,  though 
no  work  was  done  in  the  Heath  district,  where  it  occurs,  in  the  census  year. 

ALTURAS  COUNTY. — The  western  portion  of  Alturas  county,  together  with  Boise  county,  forms  a  great  granite 
district,  chiefly  drained  by  the  Boise  river  and  its  tributaries.  The  veins  in  this  granite  carry  a  quartz  gangue,  with 
gold  and  silver  ores.  In  some  the  one  metal  predominates,  in  some  the  other,  but  as  a  rule  both  are  present.  The 
ores  are  free  gold  and  auriferous  pyrite,  native  silver,  both  ruby  silver  minerals,  stephanite,  freibcrgite,  horn-silver, 
and  galena.  The  gangue  minerals  are  quartz,  pyrite,  chalcopyrite,  mispickel.  zincblende,  and  a  little  calcite, 
Molybdenite  is  also  reported.  Nearly  all  the  veins  dip  at  an  angle  of  over  45°,  and  the  majority  strike  northeast 
and  southwest,  following  the  trend  of  the  mountain  ranges. 

To  the  southeast  of  the  granite,  in  the  Wood  liiver  country,  there  are  deposits  in  limestone  of  galena  and  its 
decomposition  products,  accompanied  by  copper  and  iron  minerals.  Milling  ores  are  said  to  have  been  found  in 
the  slates  of  this  region  since  the  expiration  of  the  census  year.  There  are  also  small  placer  deposits  on  the  Salmon 
river  and  its  tributaries  in  this  county. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION. 


57 


ALTUKAS. 
.— UuUiriiiiuuiiuuB  in  parentheses  are  given  on  the  authority  of  the  experts.) 


Mine. 


WALLS. 


Ore  and  gaugue. 


Foot. 


Hanging. 


Charactet  of 
deposit 


(Gold,  galena,  antimony,  argentiferous  sulpbarsen- 
ide  and  sulphantimonide  minerals,  zincblende, 
pyrite).  quartz,  andcalcitc. 


BONAPARTE. 

Bonnpartc  Consolidated. 

IIAUD6CKAH1II.K. 

Crown  Point  Bonanza (Gold),  quartz 

Emma do 

General  Grant Gold  quartz  and  limonite 

NcwOphir Cold    quartz,   pyrite.   mispickel,  galena,   and  (zinc- 

blendej. 
MIDDLE  nOIBE. 

Jessie  jienton Kuby  silver,  quartz.   pyrite,   chalcopyrite,  (arsenical 

and  autimonial  silver  ore,  with  auriferous  pyrites). 

Buffalo (Dark  and  light  ruby  silver,  native  silver,  auriferous 

pyrites,  and  quartz.) 

Buffalo  and  Atlanta (Aoiilerons    pyrites,   argentiferous     siilpharsenide.s 

and  sulphaniimomdes,  quartz,  and  molybdenite.) 

Last  Chance Gold,  auriferous  pyrites,  ruby  silver,  and  quartz 

Monarch Dark  ruby,  horn-silver,  native  silver,  quartz,  pyrite, 

and    probably   mispickel,    (light    ruby,    auriferous 
pyi  ites,  free  gold,  and  traces  of  copper). 

Taliiuita Argentina,  an  argentiferous  sulpharseuide,   quaj-tz, 

(rnliy  silver,  native  silver,  and  a  little  free  gold). 

Ynba  Tunnel (Gold),  quartz    feldspar,  pyrite.  and  mispiekel. 

MINERAL  HILL. 

Idahoan Kicli  argentiferous  galena 

Jay  Gould Galena  and  eciussite   


Granite. 


Granite ". !  Vein. 


(Granite) . 

..-..do 

....do 

...do ... 


(Granite) 
...do... 


do. 
.do 


(Granite) (Gran  itcj . 

..  do  . .  do. .. 


do. 


do 


....do.... 
Granite. 


.do. 


(Limestone) 

...do  .. 


tlUBEN'B  KIVKR. 

Joe  Daly '  Free  gold,  quartz,  mispiekel.  and  limonite 

Mammoth Quartz   and  galena,    (native  silver,   free  gold,  light 

and  dark  ruby  silver,  and  auriferous  pyrites). 

Silver  <;laiicc Quartz  and  galena,  (stephanite,  native  silver,  light 

ruby  silver,  pyrite,  and  a  little  gold). 

Washington Quartz  and  galena,  (free  gold  and  base  sulphides) 

KI;J>  WAKBIOB. 

Donnybrook  Fair Quartz  Colorado,  (gold,  pyrite.  antimoniiil  ores.     No 

silver). 

New  York do 

Wide  West do 

Wildcat    Quartz  and  misptckcltXgold  and  silver  in  rebellions 

compounds). 

Vietor Quartz  Colorado,  (gold) 


KUCKY   BAH. 


Alt uras  Gold  Hill Gold,  quartz,  pyrite,  and  mispiekel 

Idaho- Vishnu   Gold,  galena,  quartz,  pyrite.  and  mispiekel. 


SAWTOOTH. 

Columbia Quartz,   probably   horn-silver  and  frei'nergite,  (ruby 

silver). 

Pilgrim Quartz  and  j'reiliergite  (ruby  silver.) : 

Lucky  Boy ;  Quartz  and  horn-silver 


Granite  .. 

(Granite) 

...do  .. 


.do 


...do... 
Granite 

..  do  .. 


Vein. 
Do. 
Do 
Do. 

Vein. 
Do 
Do. 

Do. 
Do. 

Do. 


(Limestone). 
Do. 


Granite Vein. 

(Grardtci !         Do. 


do 
do. 


(Granite) (Granite) 


.dp. 
.do 


do 
do 


.do 
.do. 


.do 
.do. 


Do. 
Do. 

Vein. 

Do. 
Do. 
Do. 

Do. 


Granite Granite : !  Vein. 

...do...  ...do !        Do. 


(Granite)  (Granite) !  Vein. 


.do. 
.do. 


do. 
do. 


Do. 
Do. 


BOISE  COUNTY. — This  county  is,  for  the  most  part,  in  the  grauite  area  mentioned  under  Alturas  county.  The 
veins  carry  chiefly  gold,  except  in  the  Banner  district,  where  the  silver  is  in  excess.  The  placer  deposits  of  this 
county  have  hitherto  been  the  most  important  in  the  country  outside  of  California.  Their  character  and  occurrence 
have  already  been  sufficiently  described. 


PRECIOUS  METALS. 


BOISfi. 
[NOTE — Determinations  iu  parentheses  arc  given  on  the  authority  of  the  experts.; 


Mine. 


Ore  anil  gaugue. 


Crown  Point A  sulpharscnido  of    lead,    probably  dufreynoysito, 

quartz  and  pyrite,  (ruby "silver,  horn-silver,  mis- 
pickel,  sulphur,  and  copper  compounds). 

I'aiianiint   '  Quartz,  (ruby  silver) 

CASON  CEEKK. 

i  'eiitennial !  Gold,  quartz  Colorado 

Ebenozer \  Gold    quartz,   iron    and    copper   pyrites,  and    mis- 

pickel. 


GAMimiXCS. 

Sub  Rosa Gold  quartz 

GRAMTE. 

Gold  Hill |  Quartz  and  pyrite,  (gold). 

MOORE'S  CHEEK. 

Crepisculla  Ilydranlic 

Thorn  Creek  Hydraulic 

SHAW'S  MOUNTAIN. 

North  Star. Gold  quartz  ... 

Paymaster !  (Gold)  quartz  . 


(Gold  gravel) 

..  do... 


Foot. 


Granite  diabase. 


Hanging. 


Character  of 
deposit. 


Granite 


Granite 

Granite... 


Granite  dike |  Vein. 


Granite Do. 


Granite Vein. 


Granite  ' 


Granite 


Do. 


Granite* .    Vein. 


Granite I  Granite 


Vein. 


Granite I.- I  Placer. 

..  do | Do. 


Granite Granite Vein. 


(Granite) 


Rising  Sun Gold    quartz,  galena,  copper,  pyrite,  and  probably     Granite. 

mispickel,  (fiee  sulphur). 


(Granite) 

Granite 


Do. 
Do. 


*  Microscopically  examined. 

IDAHO  COUNTY. — This  county  appears  to  contain  an  isolated  granite  area  in  tbe  neighborhood  of  Warren's 
camp  and  Florence.  The  quartz  veins  are  much  the  same  in  character  as  those  in  Bois6  county,  and  are 
accompanied  by  small  deposits  of  auriferous  gravels. 

IDAHO. 

[NOTE. — Dctermiuatious  in  parentheses  are  given  on  the  authority  of  the  experts.) 


WALLS. 

Character  of 

Foot.                                         Hanging. 

deposit. 

WARREN'S  CAJIF. 

•  ; 

Vein. 

quartz. 

LEMHI  COUNTY — The  important  mining  districts  of  Yankee  Fork,  Mount  Estes,  and  Bay  Horse  lie  in  the 
southern  portion  of  this  county.  In  the  Yankee  Fork  district  the  principal  rocks  appear  to  be  gneiss  and  an  eruptive 
which  is  possibly  rhyolite.  (The  workings  were  superficial,  and  the  specimens  were  too  much  decomposed  for 
determination.)  Free  gold  and  silver  minerals  are  accompanied  by  quartz,  pyrite,  and  copper  ores.  In  the  ]>ay 
Horse  district  the  country  rock  is  slate,  and  the  ore  consists  of  argentiferous  galena,  with  copper  minerals  and  traces 
of  gold  in  a  quartz  gaiigue. 

LEMHI. 
[  NOTE. — Determinations  in  parentheses  are  given  on  the  authority  of  the  experts.  | 


Mine. 

Ore  and  gangne. 

WALLS. 

Character  of 
deposit. 

Foot. 

Hanging. 

BAY  HORSE. 

RaniRhorn  

(Argentiferous  galena,  gray  copper,  a  little  chloride 
and  bromide  ol  silver,  copper  carbonates,  traces  of 
gold,  hematite  and  quartz.) 

(Slate) 

Vein. 

Vein. 
Do. 

Do. 

YANKEE  FOBK. 

Charles  Dickens  

General  Cuater  

Quartz,  pyrite,  and  probably  stephanito,  (argentite). 
Same  as  General  Cnster  

Indetermiuablv  decomposed 
yellow  porphyry  (locally 
called  rhyolite). 

—  do  

Vnknown  

...  do  

*  Microscopically  eiamiuod. 


GEOLOGICAL  SKETCH  OF  THE  PACIFIC  DIVISION.  59 

OWVIIEK  rpvNTY. — The  mining  districts  of  Owyhee  county  lie  about  Silver  City  and 'Wagontown,  on  the 
Jordan  river.  This  region  is  separated  from  the  granite  region  of  Alturas  and  Boise  counties  by  the  Quaternary 
plains  of  Ada  county,  but  it  is  extremely  probable  that  the  granite  of  Silver  City  is  a  portion  of  the  larger  mass 
to  the  north.  To  the  southwest  of  Silver  City  the  surface  is  occupied  by  quartz-porphjry  overlying  metamorphic 
rocks  in  part,  and  both  porphyry  and  granite  are  intersected  by  dikes  of  basalt.  The  ores  are  similar  to  those  of 
the  northern  granitic  area:  gold,  silver,  freibergite,  and  sulphurets  in  a  quartz  gangue.  The  veins  follow  the  general 
trend  of  the  mountains  to  the  northwest  and  dip  at  high  angles.  As  usual,  small  placers  accompany  the  gold  veins. 

In  the  South  Mountain  district,  near  the  Oregon  line,  galena  occurs  in  limestone.  Coal  has  been  found,  but 
only  in  insignificant  quantities.  Tinstone  has  been  identified  as  float  in  the  Jordan  river. 

OWTHEE. 
[NOTE.—  Determinations  in  p-renthesos  are- given  on  the  authority  of  the  experts.) 


WALLS. 


Character  of 

Foot. 

deposit. 
Hanging. 

CARSON. 

Black  Jack                  

• 

calc-spar,  cupper  stains). 

(Granite) 

(Granite)                       Do 

Florida  Hill              

IdlewiUl 

(Five  gold  and  argentiferous  sulphurets,  quartz) 

.   'do 

do                         Do 

Granite                             ....           Do 

Rath  
AV;ir  Ea""lr 

ProbaUy  arg«  ntite,  quartz  

Granite  of  somewhat  gneis- 
soid  structure. 

(Granite) 

Gninitt-  of  somewhat  gneifl-          Do. 
sold  structure. 

(Granite)                           ••   •  •         Do 

WA<;O.NTOWN. 

Ohio 

deteniiinabta,  quartz. 

(Porphyry)                                       Do 

Web  foot 

(Porphyry)                                       Do 

Microscopically  examined. 


OTHER   COUNTIES, 

In  Oneida  county  gold  quartz  veins  and  placers  are  worked  at  Cariboo  and  Iowa  Bar,  and  along  the  course  of 
the  Snake  river  in  this  and  Cassia  counties  gold  washings  are  conducted  on  a  small  scale. 

The  northern  counties  of  Kootenai,  Nez  Perce",  Shoshone,  and  Washington  contain  gold  quartz  veins  and 
placers,  which  are  not,  however,  worked  to  any  considerable  extent,  and  the  conditions  of  their  occurrence  are  not 
known. 

Salt  and  sulphur  are  obtained  in  Bear  Lake  county. 


60  PRECIOUS  METALS. 


.CHAPTER  II.— GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION. 

BY  S.  F.  EMMONS. 

lu  the  following  pages  the  writer  has  endeavored  to  present  u  brief  outline  of  the  geological  structure  of  the 
states  and  territories  of  this  division  as  far  as  it  bears  on  the  ore  deposits  of  the  region,  the  geological  occurrences 
of  the  ore  deposits  themselves,  and  their  mineralogical  composition  as  far  as  it  has  been  possible  to  determine  them. 
Such  a  sketch  at  the  present  time  must,  from  the  nature  of  things,  be  extremely  unequal,  and,  at  its  best,  very 
incomplete;  but  it  has  seemed  best  to  give  it  in  this  incomplete  form,  even  if  it,  merely  serves  to  show  the  gaps 
in  our  knowledge  and  to  encourage  others  to  fill  them  up.  The  importance  of  the  geological  relations  of  mineral 
deposits  has  been  hitherto  very  much  underestimated,  chiefly  for  the  reason  that  so  few  competent  men  have  given 
attention  to  their  study.  For  this  reason  geological  literature  contains  but  little  trustworthy  information  on  this 
subject. 

The  material  here  presented  has  been  in  part  compiled  from  data  and  specimens  gathered  by  census  experts, 
and  in  part  from  reports  of  government  surveys,  from  reports  by  individual  geologists  upon  mining  districts, 
unfortunately  too  few  in  number,  and  from  the  personal  observations  of  the  writer  in  portions  of  Wyoming  and 
Colorado.  There  was  difficulty  in  obtaining  men  who  had  at  the  same  time  a  knowledge  of  field  geology  and  a 
practical  acquaintance  with  mines,  and  the  limited  time  at  the  disposal  of  those  to  whom  the  work  was  intrusted 
rendered  it  practically  impossible  to  visit  every  mining  district.  Of  the  specimens  of  ore,  gangue,  and  country 
rock  which  it  was  intended  should  be  obtained  from  each  mine  a  large  proportion  were  in  a  too  far  advanced 
stage  of  decomposition  for  satisfactory  determination.  In  many  cases  no  specimens  accompanied  the  schedules. 
Hence  the  tables  of  mines,  country  rocks,  and  ores  which  accompany  the  following  sections  are  incomplete  in 
many  important  instances;  but  it  has  not  been  thought  advisable  for  that  reason  to  refrain  from  publishing  them, 
even  in  their  imperfect  condition,  since  they  contain  many  data  useful  to  mining  engineers,  and  will  serve  as  a 
skeleton  which  may  hereafter  be  more  completely  clothed  as  additional  material  is  obtained.  In  cases  where  no 
specimens  were  at  hand  it  is  indicated  in  the  table,  the  information  given  being  on  the  authority  either  of  the 
experts  themselves  or  of  some  person  connected  with  the  mine.  At  the  end  of  another  decade  it  is  hoped  that  our 
knowledge  of  these  important  mining  regions  will  be  such  as  to  render  it  possible  to  present  the  information  which  is 
here  outlined  in  a  comparatively  complete  form. 

The  maps  which  accompany  these  sketches  are  intended  as  a  guide  to  the  reader  unacquainted  with  the 
geography  of  the  country,  and  will  serve  to  show  those  who  are  already  somewhat  familiar  with  it  the  county 
divisions,  which  have  been  followed  in  the  treatment  of  each  section.  An  attempt  has  also  been  made,  in  a  very 
general  way,  to  iiMlicate  by  colored  dots  the  relative  distribution  among  actually  producing  mines  of  ores  in  which 
gold  or  silver  predominate.  These  are  given,  as  well  as  the  rest  of  the  material,  rather  as  a  sketch  than  as  a  finished 
and  accurate  delineation. 

GEOLOGICAL  SKETCH  OF  COLORADO. 

The  state  of  Colorado,  which  is  included  between  the  .'J7th  and  41st  degrees  of  north  latitude  and  the  25th  and  3Hd 
degrees  of  longitude  west  from  Washington,  has  an  area  of  103,045  square  miles.  This  area  may  be  divided  into 
three  meridional  belts:  a  plain  belt,  comprising  a  little  over  one-third  of  the  eastern  portion  of  the  state;  a 
mountain  belt,  lying  next  west  of  the  former,  and  covering  also  about  one-third  of  the  state ;  and  a  narrower  belt 
on  the  west,  which  is  largely  a  mesa  country,  and  belongs  to  the  so-called  Colorado  plateau  region. 

According  to  the  classification  of  Lieutenant  Wheeler's  maps,  only  about  one-fifteenth  of  the  whole  surface  is 
arable  land,  but  at  the  time  this  classification  was  made  probably  only  the  alluvial  bottom  lauds  of  the  larger 
streams  were  assumed  to  be  available  for  agricultural  purposes.  This  restriction  may  hold  good  for  the  mesa  region, 
but  with  the  late  rapid  increase  in  the  population  of  the  state  increasing  areas  of  plain  country  to  the  east  of  the 
mountains  have  been  brought  under  cultivation  by  means  of  irrigating  ditches,  and  the  results  obtained  have  shown 
that  the  soil  is  exceptionally  favorable  to  agriculture,  the  extent  to  which  it  can  be  profitably  carried  on  being 
probably  limited  only  by  the  feasibility  of  irrigation.  A  large  portion  of  the  plain  country  is  covered  by  a  porous, 
crumbling,  homogeneous  soil,  filling  irregularities  of  the  rock  surface  beneath  to  depths  of  from  5  to  20  or  more- 
feet,  whose  external  appearance  strongly  resembles  that  of  the  famous  loess  which  has  proved  the,  source  of 
fertility  of  many  important  agricultural  regions  in  the  world. 

As  yet  no  systematic  studies  have  been  made  of  the  geology  of  the  plain  country,  and  the  actual  extent  and 
eh;ir;>rfor  of  this  deposit  is  not  definitely  known.  It  seems  probable,  however,  that  it  may  at  least  be  analogous 


•GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  61 

to  tin-  loess  \vliidi  hns  been  proved  to  exist  farther  east,  in  Nebraska  and  Kansas.  An  analysis  of  this  soil, 
taken  from  the  neighborhood  of  Golden,  close  to  the  foot-hills  of  the  mountains,  made  in  the  laboratory  (.r  the  I'nited 
States  geological  survey  at  Denver,  gave  the  following  results: 

IVr  rent 

sili<il 72.si2 

A)ninii:a 12.  (ji>4 

Scsi|iiiosi«le  of  iron  .., I.  t;;;!i 

Lil1"' 1.14? 

Magnesia ;..  Q.944 

Potash 3.748 

Soda '2.472 

Water  and  organic  matter 1_  79; 

Phosjiliorir  acid 0. 228 


09.  981 

The  lime  and  magnesia  in  this  soil  are  in  considerably  smaller  proportions  than  in  ordinary  loess  soils,  but  at 
least  50  per  cent,  of  the  material  may  be  supposed  to  be  free  quartz.  It  may  be  assumed,  therefore,  that  at  a  greater 
distance  from  the  mountains  the  proportion  of  silica  will  be  smaller,  and  the  more  soluble  and  easily  transportable 
salts  greater.  The  same  soil  about  10  miles  to  the  east  of  Denver,  or  20  miles  from  the  foot  of  the  mountains, 
yielded  4.5  per  cent,  of  lime  and  0.8  per  cent,  of  magnesia  in  a  soluble  form,  probably  as  carbonate. 

The  climate  of  Colorado  is  essentially  a  dry  one,  though  less  so  than  that  of  New  Mexico.  In  summer  there 
are  often  showers,  but  they  are  too  uncertain  to  be  depended  on  for  agricultural  purposes. 

ARTESIAN  WKLLS. — The  extent  to  which  agriculture  may  be  carried  on  is  therefore  dependent  mainly  upon  the 
amount  of  water  which  isavailable  for  purposes  of  irrigation.  The  various  streams  which  emerge  from  the  mountains 
yield  a  sufficient  supply  for  a  comparatively  narrow  belt  along  the  foot-hills,  but,  owing  to  the  rapid  evaporation 
which  takes  place  in  this  dry  climate,  they  cannot  be  counted  on  for  irrigating  the  lands  at  any  great  distance  to 
the  eastward. 

Artesian  wells  have  been  suggested  as  another  source  of  supply,  and  government  aid  has  been  called  in  to 
make  practical  experiments,  with  a  view  to  determining  whether  these  wells  will  yield  water  in  sufficient  amount  for 
purposes  of  irrigation.  The  water  supply  of  artesian  wells  is  supposed  to  follow  the  laws  of  hydrostatic  pressure: 
that  is,  where  the  surface  water,  penetrating  the  earth  from  the  surface,  reaches  an  impermeable  stratum,  it  follows 
the  inclination  of  that  stratum  as  an  underground  stream.  If,  then,  this  stratum  be  reached  by  an  artesian  boring 
at  a  point  where  the  surface  of  the  ground  is  sufficiently  below  the  outcrop  of  that  stratum,  the  water,  seeking  its 
original  level,  will  flow  out  through  this  boring  to  the  surface.  The  structural  conditions  on  the  great  plains  are 
theoretically  favorable  for  obtaining  flowing  wells.  The  sedimentary  formations  which  underlie  them  are  upturned 
at  their  western  edge  against  the  foot-hills  of  the  mountains,  and  are  thus  accessible  to  the  waters  which  drain  their 
surface.  The  surface  of  the  plains  slopes  regularly  to  the  eastward,  although  at  a  very  gentle  angle;  so  that  to 
obtain  the  required  difference  of  level  it  will  be  necessary  to  go  some  distance  from  the  mountains,  as  it  is  found  in 
practice  that  the  water  from  artesian  wells  does  not  strictly  fulfill  the  condition  of  finding  its  own  level,  but  that  a 
certain  portion  of  the  difference  of  elevation  is  lost  probably  by  friction  and  the  want  of  a  perfectly  free  underground 
circulation.  Of  the  sedimentary  formations  the  Tertiary  beds  lie  horizontal  and  are  not  upturned,  and  these,  owing 
to  their  porous  character,  probably  would  not  carry  the  required  supply  of  water.  It  is  advisable,  therefore,  to  avoid 
sinking  the  wells  where  these  still  exist,  and  fortunately  their  present  area  is  probably  limited.  Of  the  Mesozoic 
beds,  the  upper  formations  (the  Cretaceous)  are  largely  composed  of  sandstones,  which  are  also  porous  and  more  or 
less  permeable  to  water.  They  contain  also,  it  is  true,  beds  of  clay,  but  it  cannot  be  certainly  stated  that  these 
clay  beds  are  continuous  over  any  great  areas.  It  is  questionable,  therefore,  if  the  Cretaceous  formation  will  yield 
a  large  supply  of  water,  except  locally,  as  near  Denver,  where  a  synclinal  basin  is  formed  by  a  slight  fold  in  tin- 
strata  to  the  east  of  it.  In  the  Jura,  below  the  Cretaceous,  the  conditions  seem  more  favorable,  as  they  contain 
a  considerable  amount  of  clay  and  a  comparatively  persistent  limestone  bed.  The  Trias  is  a  formation  largely 
of  sandstones,  and  therefore  not  favorable,  and  it  is  only  when  the  Carboniferous  is  reached,  which  is  made  up  of 
compact  and  evenly-bedded  limestone,  that  we  come  to  strata  which  arc  beyond  doubt  capable  of  carrying  the 
required  supply  of  water.  The  thickness  of  these  different  formations  has  not  yet  been  accurately  determined  ;  but 
it  may  be  assumed  at  the  foot-hills  that  the  Cretaceous  beds  are  at  least  3,000  feet  in  thickness,  and  the  Jura  and 
Trias  2,000  more,  [t  will  be  seen,  therefore,  that  it  may  require  a  boring  5,000  feet  in  depth  to  give  a  permanent 
and  considerable  flow  of  water.  On  the  other  hand,  there  arc  good  grounds  for  supposing  that  the  thicknesses  of  t  he 
different  formations  decrease  to  the  eastward,  and  this  supposition  has  been  in  part  continued  by  actual  observation 
along  a  line  near  the  southern  border  of  the  state.  It  is  probable,  therefore,  that  at  a  sufficient  distance  to  the 
eastward  the  thickness  of  the  beds  overlying  the  Cretaceous  formation  will  be  very  much  less  than  the  figures  above 
given.  In  the  present  state  of  our  knowledge  these,  are  largely  matters  of  conjecture,  and  it  is  only  by  the  actual 
experiment  of  boring  wells  that  the  thickness  and  water-bearing  properties  of  the  different  formations  can  be 
determined.  It  is  evident,  however,  from  what  has  been  said,  that  these  experimental  well*  should  be  sunk  near 
the  eastern  border  of  the  state,  and  at  points  where  the  greatest  thie.kin.-ss  of  the  upper  beds  is  likely  to  have 


62  PRECIOUS  METALS. 

been  removed,  bringing  the  deep-seated  water-currying  bed,  therefore,  nearest  Hie  present  surfaces.  To  determine 
these  points  with  accuracy,  however',  would  require  an  accurate  and  systematic  topographical  and  geological  survey, 
which  has  not  yet  been  made,  and  the  choice  of  the  right  location  must  be  largely  a  matter  of  chance.  It  seems 
probable,  therefore,  that  with  its  exceptionally  favorable  conditions  of  climate  and  a  soil  of  this  character  the 
agricultural  resources  of  Colorado  are  yet  but  partially  developed. 

COAL — Its  industrial  possibilities,  if  gauged  by  its  natural  resources  in  coal,  the  indispensable  basis  of  almost 
every  industrial  enterprise,  are  almost  unlimited,  not  less  than  two-thirds  of  the  area  of  the  state  being  underlaid  by 
the  coal  formation.  While  over  a  great  portion  of  this  area  it  may  lie  too  deep  for  profitable  extraction,  and  while 
coal  beds  are  by  no  means  necessarily  continuous  in  any  particular  formation  over  very  large  areas,  yet  the  geological 
conditions  are  such  that  a  relatively  large  proportion  of  this  formation  is  brought  to  the  surface  and  rendered 
available  for  practical  working,  especially  along  the  borders  of  the  mountain  belt.  Along  the  eastern  front  coal 
mines  are  already  opened  and  working  at  intervals  from  the  northern  to  the  southern  boundary  of  the  state. 
Mines  are  also  worked  in  the  South  park,  in  the  center  of  the  mountain  belt,  and  in  Guunison  and  La  Plata 
counties,  on  the  western  slope,  while  the  developments  in  many  other  localities  are  only  awaiting  railroad 
communication  and  an  industrial  demand. 

•  MOUNTAIN  BELT. — The  precious-metal  production  of  the  state  is  derived  mainly  from  the  mountain  belt,  as 
might  have  been  assumed  on  a  priori  geological  grounds,  reasoning  from  which  none  would  be  looked  for  in  the 
plain  country;  nor  wo1  aid  much  be  expected  from  the  mesa  region,  except  where  eruptive  rOcks  have  protruded 
through  the  sedimentary  strata  and  formed  such  isolated  mountain  groups  as  the  Sierra  la  Sal,  Sierra  Abajo, 
Sierra  el  Late,  and  others.  The  topography  of  the  mountain  region  and  the  plateau  country  on  its  west,  as  well 
as  its  general  geological  structure,  is  pictured  on  the  maps  of  the  Hayden  survey,  of  which  the  extreme  northern 
strip  is  taken  from  those  of  the  Fortieth  Parallel.  The  most  important  group  of  rocks  there  represented,  and 
intimately  connected  with  ore  deposition,  viz,  those  of  Mesozoic  or  Secondary  age,  have  either  entirely  escaped 
recognition  or  have  been  classed  indiscriminately  as  belonging  either  to  the  volcanic  rocks  or  to  granites. 

The  mountain  belt  of  Colorado,  which  in  this  latitude  is  generally  known  as  the  Rocky  mountains,  to  distinguish 
it  from  the  other  principal  Cordilleran  systems  to  the  westward,  the  Wahsatch  and  the  Sierra  Nevada,  has,  taken  as 
a  whole,  a  due  north  and  south  trend.  When  examined  in  detail,  however,  it  is  found  to  be  made  up  of  a  number  of 
more  or  less  regular  chains  or  ridges  having  a  general  trend  to  the  west  of  north,  standing  en  echelon  or  with  their 
ends  overlapping  each  other,  with  mountain  valleys  of  greater  or  less  extent  between  them,  as  the  result  of  which 
structure  the  mountains  in  general  seem  to  be  divided  up  into  two  chains,  with  large  included  valleys  which  have 
received  the  name  of  "parks".  The  general  name  of  Colorado,  or  Front,  range  has  been  given  to  the  eastern  of 
these  divisions,  and  that  of  Park  range  to  the  western.  The  North,  Middle,  and  South  parks  and  the  San  Luis 
valley  are  the  larger  of  the  included  valleys,  the  three  former,  with  the  smaller  Wet  Mountain  valley  to  the  south, 
being  really  a  portion  of  the  same  continuous  line  of  depression,  while  the  valley  of  the  Upper  Arkansas  stands 
in  the  same  relation  to  the  San  Luis  valley.  The  eastern  front  of  this  range  presents  a  comparatively  regular  north 
and  south  line,  broken  here  and  there  by  bay-like  valleys,  running  up  into  the  mountains  in  a  northwesterly  direction 
arid  following  the  prevailing  trend  of  the  echelon  ridges.  The  most  important  of  these  are  the  Manitou  and  Huerfano 
parks  and  that  which  extends  up  Oil  creek  from  Canon  City.  These  in  earlier  geological  times  were  actual  bays 
in  the  seas  in  which  the  Palaeozoic  and  Mesozoic  rocks  were  deposited,  while  the  parks  were  partially  inclosed 
arms  of  those  seas. 

The  western  front  of  the  mountains  is,  however,  much  more  irregular,  and  is  broken  by  branching  mountain 
groups  extending  out,  also  with  a  general  northwest  trend,  into  the  mesa  coujitry  of  the  Colorado  plateau.  The 
principal  of  these  outlying  mountain  groups,  commencing  on  the  north,  are  the  Elk  Head  mountains,  the  White 
River  plateau,  the  Elk  mountains,  and  the  San  Juan  mountains,  in  all  of  which,  as  will  be  seen  later,  there  is  a  very 
great  development  of  eruptive  rocks. 

GEOLOGY. — The  geological  history  of  this  mountain  region  is,  briefly  and  in  its  most  general  outlines,  as  follows : 
At  the  close  of  the  Archaean  era,  or  in  the  Cambrian  ocean,  a  large  area,  covering  most  of  what  is  now  the  Colorado 
range,  formed  a  large  rocky  island,  with  a  number  of  minor  islands  lying  to  the  westward,  the  most  important  of  which 
was  that  which  now  forms  the  Sa watch,  from  which  it  was  more  or  less  completely  separated  by  the  waters  occupying 
the  present  depressionsof  the  North,  South,  and  Middle  parks.  During  the  whole  of  the  Paleozoic  and  Mesozoic  eras 
a  continuous  sedimentation  went  on  in  the  seas  surrounding  these  islands  of  material  derived  from  their  abrasion. 
The  geological  record,  as  far  as  it  has  been  studied  at  the  present  day,  gives  evidence  of  no  great  disturbance  during 
this  long  period,  although  it  is  probable  that  local  elevation  and  subsidence  might  have  taken  place;  and  there  is 
some  evidence  to  show  a  general  subsidence  of  the  whole  area,  which  gave  a  somewhat  larger  field  of  deposition  to 
the  later  sediments  of  these  periods.  Toward  the  close  of  the  Cretaceous  period,  at  the  time  of  the  formation  of  the 
coal  beds,  the  seas  became  shallower,  owing  to  a  general  elevation  of  land,  and  considerable  portions  of  the  outlying 
areas  were  partially  inclosed.  During  this  time,  and  possibly  earlier,  immense  masses  of  eruptive  rock  were  forced  up 
through  the  already  deposited  sediments  which  were  still  beneath  the  water.  Unlike  the  lava  flows  of  modern 
•  lays,  however,  these  molten  masses  were  not,  as  a  rule,  spread  on  the  surface  of  the  rocks,  but  congealed  before 
they  reached  it,  either  in  large  masses,  in  dikes,  or  in  sheets  spread  out  between  the  beds.  It  is  impossible  to  say 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  63 

li'.»\v  long  before  (lie  close  of  the  Cretaceous  period  the  eruption  of  these  Secondary  igneous  rocks  commenced,  but 
it  is  known  that  in  certain  localities  it  must  have  continued  nearly  to  the  close  of  the  period.  At  some  time  after 
the  close  of  the  Cretaceous  period  a  general  dynamic  movement  took  place  in  the  Rocky  mountains,  by  which  tin- 
existing  mountain  ranges  or  islands  were  crushed  together,  broken,  and  elevated,  and  considerable  areas  of  the 
adjoining  sea-bed  were  lifted  above  its  surface.  In  the  general  continental  elevation  which  followed  fresh-water 
lakes  or  inclosed  seas  were  formed,  in  which,  by  the  degradation  of  the  newly-made  land  areas,  considerable 
sediments  were  deposited.  The  outlines  of  these  Tertiary  seas,  owing  to  the  nature  of  the  deposits  made  in  them, 
which  were  easily  eroded  and  carried  away  by  subsequent  atmospheric  agencies,  cannot  be  yet  definitely  determined. 
It  can  only  be  said  that  their  area  and  location  were  frequently  changed,  and  that  during  the  Tertiary  era,  and 
subsequent  to  it,  eruptions  of  igneous  rock  occurred,  generally  following  the  lines  of  earlier  eruptions,  but,  unlike 
those,  spreading  out  on  the  actual  surface  of  the  land,  and  in  some  cases  beneath  the  sea.  While  the  general 
form  of  the  mountain  area,  as  has  been  shown,  was  determined  iu  the  very  earliest  geological  times,  it  is  only 
since  the  Tertiary  era,  and  in  a  great  measure  by  erosion  subsequent  to  the  Glacial  period,  that  the  present 
sculpturing  of  the  mountain  forms  and  carving  of  the  valleys  have  taken  place.  At  what  period  during  this  history 
the  different  mineral  deposits  of  Colorado  were  formed  it  is  as  yet  impossible  to  say  with  any  degree  of  definiteness. 
The  gold  deposits  of  Gilpin  county  in  the  Archaean  may,  like  those  of  the  Black  hills  of  Dakota,  be  of  pre- 
Cambrian  age.  It  is  probable,  however,  that  some  of  these  at  least,  and  the  silver  deposits  iu  the  adjoining  counties 
of  Clear  Creek  and  Boulder,  were  subsequent  to  the  intrusion  of  the  porphyries,  which  are  presumably  of  later  date. 
The  silver  deposits  of  Leadville  are  known  to  have  been  formed  subsequent  to  the  Carboniferous  and  previous  to  the 
dynamic  movement  at  the  close  of  the  Cretaceous.  Some  of  the  silver  deposits  of  Guunison,  on  the  other  hand, 
must  have  been  later  than  the  Cretaceous,  while  those  of  Custer  county  and  the  San  Juan  region  are  in  part  at 
least  presumably  of  post  Tertiary  age. 

ORES. — The  ores  of  Colorado  present  an  almost  infinite  variety  of  miueralogical  composition,  so  that  it  is  difficult 
to  formulate  any  general  laws  with  regard  to  their  distribution  or  manner  of  occurrence.  Of  the  actual  precious- 
metal  production  of  the  state,  by  far  the  largest  portion  is  derived  from  pyrites  and  galena  and  their  decomposition 
products.  The  telluride  ores  of  Boulder  county  and  the  auriferous  pyrites  of  Gilpin  county,  with  a  few  individual 
deposits  in  the  southern  portion  of  the  state,  constitute  the  source  from  which  its  gold  is  derived.  With  these 
exceptions  its  mineral  deposits  may  be  considered  as  essentially  silver-bearing.  The  principal  source  of  silver,  as 
has  already  been  stated,  is  argentiferous  galena  and  its  decomposition  products,  while  argentiferous  gray  copper, 
or  freibergite,  is  next  to  this  the  most  important  silver-bearing  mineral.  The  sulphides  of  silver  also  occur,  and 
in  some  cases  bismuth  is  found  in  sufficient  quantity  to  constitute  an  ore.  As  yet,  so  far  as  known,  no  copper  is 
extracted  from  the  ores  of  the  state,  except  as  an  adjunct  in  the  reduction  of  silver-bearing  copper  ores.  Placer 
deposits  are  generally  confined  to  the  valley  bottoms  among  high  mountain  ridges,  and  while  they  are  locally  of 
considerable  value  and  importance,  and  were  the  original  attraction  which  brought  the  mining  community  to  the  state, 
their  present  yield  forms  a  very  inconsiderable  proportion  of  its  precious-metal  production.  Prior  to  the  discovery  of 
the  silver  ores  of  Leadville  mining  in  the  state  was  principally  confined  to  approximately  vertical  veins  either  in  the 
Archaean  rocks  of  the  Front  range  or  the  eruptive  rocks  of  the  San  Juan  region  ;  but  since  the  limestone  deposits  of 
the  Mosquito  range  have  proved  so  exceptionally  rich  the  attention  of  prospectors  has  been  more  and  more  turned 
to  the  ores  which  occur  in  sedimentary  rocks,  and  many  new  districts  have  been  discovered,  but  none  to  rival  that 
of  Leadville. 

As  regards  geological  distribution,  gold  is  found  in  the  Archaean  and  in  the  eruptive  rocks  of  the  Secondary  age. 
In  the  sedimentary  formations  it  is  comparatively  rare  in  limestone  beds,  but  is  not  infrequent  in  siliceous  beds. 
Silver  is  also  found  in  the  Archaean  and  in  the  Secondary  eruptive  rocks.  In  the  sedimentary  beds,  on  the  other 
hand,  it  is  more  common  in  the  limestones,  although  it  is  not  exclusively  confined  to  them.  By  far  the  greater 
portion  of  this  metal  produced  in  the  state  is  derived  from  the  limestones  of  the  Palaeozoic  formations. 

The  most  important  generalization  to  be  made  with  regard  to  the  distribution  of  ore  deposits  is  one  that  has 
been  already  noted  in  other  countries,  viz,  that  the  largest  and  most  important  ore  deposits  are  found  where  igneous 
rocks  are  most  abundant.  The  experience  of  the  writer  leads  "him  to  further  modify  this  by  saying  that  it  is  the 
eruptive  rocks  of  earlier  age  than  the  Tertiary  volcauics  with  which  valuable  ore  deposits  are  generally  associated. 

The  mineral  wealth  of  the  state  is  by  no  means  confined  to  the  precious  metals.  Its  coal  beds  are  widespread, 
and  contain  both  bituminous  and  anthracite  coals.  Gypsum  beds  are  of  frequent  occurrence  in  the  Triassic  and 
Upper  Carboniferous  formations,  and  salt  springs  are  not  infrequent,  and  probably  derive  their  supply  from  the  same 
horizon.  The  Dakota  group  of  the  Cretaceous  on  the  eastern  foot-hills  carries  beds  of  most  remarkably  pure  fire- 
clay. Excellent  building-stone  is  quarried  from  the  Archaean,  which  furnishes  red  granite ;  from  the  Mesozoic 
formations,  which  furnish  white  and  red  sandstones  and  valuable  fiags ;  and  from  the  tufaceons  rhyolite-lava  beds 
of  the  plains. 


04  PRECIOUS  METALS 

KA  STERN  COUNT!  K*. 

Weld,  Arapahoe,  Blbert,  and  Bent  counties,  and  the  eastern  portion  of  Las  Animas,  lie  entirely  in  the  plain 
region  east  of  the  mountains.  Their  surface  is  covered  to  a  depth  of  from  10  to  20  feet  by  a  light,  porous,  almost 
loess-like  soil,  which  is  admirably  adapted  to  agriculture  wherever  it  is  possible  to  bring  water  for  purposes  of 
irrigation.  Where  this  is  not  possible,  the  natural  grasses  arc-  most  valuable  for  the  raising  of  stock.  No  metallic 
minerals  are  to  be  looked  for  in  this  region,  but  it  is  underlaid  by  the  rocks  of  the  coal  formation,  which  must  contain 
extensive  and  valuable  beds  of  this  mineral,  whose  development  is  only  dependent  on  the  market  demands  and  the 
depth  below  the  surface  at  which  it  occurs. 

LARIMER  COUNTY. 

This  county  includes  the  northern  end  of  the  Colorado  range  in  Colorado,  and,  although  mostly  a  mountain 
district,  has  as  yet  developed  no  considerable  mineral  wealth.  One  reason  of  this  may  be  found  in  the  fact  that 
the  range  is  here  mainly  made  up  of  Archaean  granite — a  coarse,  red,  crumbling  rock,  which  is  characteristically 
developed  at  Sherman,  on  the  Union  Pacific  railroad,  and  which  has  in  this  state  thus  far  proved  barren  of 
metallic  minerals.  A  lurther  reason  may  be  found  in  the  comparatively  limited  development  of  Secondary  eruptive 
rocks,  which,  so  far  as  known,  occur  only  in  the  western  limits  of  the  country  bordering  on  the  North  park,  at  the 
head  of  Grand  river.  Mines  have  already  been  discovered  near  the  western  boundary  of  the  county,  at  the 
head  of  Laramie  river,  in  the  Medicine  Bow  range. 

GRAND  COUNTY. 

This  county  includes  the  North  and  Middle  parks,  whose  surface  is  mainly  covered  by  Mesozoic  rocks,  and 
are  separated  by  a  cross-range  of  eruptive  porphyry  and  volcauics.  In  the  Archaean  mountains  which  inclose  the 
county,  and  still  more  in  the  eruptive  range  which  divides  the  two  parks,  the  geological  conditions  are  favorable 
for  the  formation  of  valuable  deposits  of  minerals.  As  yet,  however,  owing  to  the  difficulty  of  access  and  want  of 
railroad  connection,  no  important  mines  have  been  developed,  and  data  from  the  few  mining  districts  that  exist 
within  the  county  are  entirely  wanting.  The  coal-bearing  formations  originally  covered  the  greater  part  of  both 
park  areas,  but  these  have  been  removed  in  part  by  erosion. 

ROUTT  COUNTY. 

This  county,  which  extends  from  Grand  county  west  to  the  Utah  line,  comprises  the  valleys  of  the  Tampa  and 
of  the  Little  Snake  rivers,  which  are  underlaid  by  coal  rocks,  whose  deposits  come  to  the  surface  along  the  borders, 
but  in  the  centers  are  too  deeply  buried  beneath  the  overlying  Tertiary  beds  to  be  practically  available. 
These  deposits,  as  elsewhere,  afford  no  promise  of  metallic  minerals.  In  the  bordering  mountains  the  only  known 
mineral  developments  are  the  placer  mines  of  Halm's  Peak  district,  which  are  found  in  the  angle  between  the 
Archaean  uplift  of  the  Park  range  and  the  volcanic  group  of* the  Elk  Head  mountains.  These  placer  deposits  are 
evidently  derived  from  the  disintegration  of  Archaean  rocks,  and  have  yielded  a  small  but  constant  return  for 
many  years  past.  Near  the  junction  of  the  Elk  river  with  the  Yampa  is  an  extremely  interesting  group  of  mineral 
springs  carrying  sulphur  and  free  carbonic  acid,  known  as  the  Steamboat  springs.  The  coal-bearing  Cretaceous 
formations  occupy  the  valley  of  the  Yampa  river  and  a  great  part  of  the  ridge  which  divides  it  from  the  White 
river  on  the  south.  Favorably  situated  outcrops  are  abundant,  and  only  await  the  advent  of  railroads  to  become  of 
practical  value. 

BOULDER  COUNTY. 

TOPOGRAPHICAL. — The  mines  of  Boulder  county  are  situated  on  the  eastern  slope  of  the  Colorado  or  Front 
range,  not  far  from-  the  town  of  Boulder,  which  lies  at  the  month  of  Boulder  canon  where  it  debouches  on  the  plains. 
The  district  containing  the  mines  extends  about  13  miles  in  a  north  and  south  direction,  and  from  4  to  10  miles  from 
east  to  west. 

The  country  is  drained  by  a  number  of  creeks,  which  cut  deep  canons  between  the  mountain  spurs.  These  are, 
commencing  on  the  north,  the  south  branches  of  Saint  Vrain  creek,  then  James  (popularly  Jim)  and  Left-hand 
creeks,  which  join  a  little  below  Jamestown  and  flow  out  on  the  plains,  as  Left-hand  creek,  into  the  Saint  Vrain  at 
Longmont;  next  the  various  forks  of  Boulder  creek  (Four-mile,  North  Boulder,  and  Middle  Boulder),  which  flow 
past  the  town  of  Boulder  in  a  single  stream,  and  also  are  tributary  to  Saint  Vrain  creek. 

The  town  of  Boulder  is  connected  by  the  Colorado  Central  railroad  with  Denver  on  the  south  and  Cheyenne 
on  the  north,  and  by  the  Boulder  Valley  railroad  with  the  Denver  Pacific  railroad.  A  narrow-gauge  railroad  is 
also  projected  from  Denver  to  run  up  into  the/mountains  via  Boulder.  There  are  a  number  of  small  mining  districts 
in  this  region  whose  limits  were  not  definitely  ascertained,  but  they  are  not  in  themselves  important,  except  for 
purposes  of  descript ion.  The  mines  on  the  Saint  Vrain  are  generally  included  in  the  Saint  Vrain  district.  On 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  65 

James  creek  is  the  Central  district.  South  of  Left  hand  creek  is  the  Gold  Hill  district,  with  the  Sunshine  district 
nearer  the  foot-hills,  and  at  the  head  of  this  creek  is  the  Ward  district.  Still  south  of  this,  between  Four-mile  creek 
and  North  Boulder,  is  the  Sugar-loaf  district,  and  south  of  Boulder  creek  Magnolia  district,  while  at  the  head  of 
Middle  Boulder  creek  is  Caribou  or  Grand  Island  district. 

GEOLOGICAL. — The  general  geological  structure  of  the  district  is  simple  and  typical  of  the  mining  districts 
on  the  eastern  slope  of  the  Colorado  range.  Along  the  foot-hills  immediately  adjoining  the  plains  is  a  series  of 
so-called  hog-backed  ridges,  formed  by  upturned  Mesozoic  strata  resting  on  the  Archaean  core  of  the  range.  These 
upturned  sedimentary  beds  form  a  fringing  belt,  of  a  width  varying  with  their  angle  of  dip,  along  the  entire  extent  of 
the  eastern  foot-hills.  Just  south  of  Boulder  their  angle  is  almost  vertical,  and  they  form  a  prominent  peak,  rising 
to  au  elevation  of  over  8,000  feet,  or  3,000  feet  above  the  plains.  The  upper  member  of  the  sedimentary  series, 
the  Laramie  or  Lignitic  group,  contains  valuable  coal  deposits,  whose  outcrops,  by  erosion  at  Boulder,  have  been 
moved  out  some  distance  on  the  plains.  Besides  coal,  these  beds  furnish  admirable  building-stone  and  flagging, 
and  also  fire-clay  and  lime.  Of  metallic  minerals,  however,  they  have  as  yet  proved  barren.  The  Archaean  rocks 
immediately  adjoining  the  plains  have  generally  been  found  to  contain  but  few  valuable  minerals,  and  it  is  not 
antil  the  range  has  been  penetrated  for  a  distance  of  several  miles  that  prominent  deposits  appear. 

In  Boulder  county  the  mines  are  found  within  2  miles  of  the  plains.  The  Archiean  rocks  of  the  Boulder  district 
consist  mainly  of  gneiss,  intersected  by  veins  of  pegmatite  (or  coarse-grained  secondary  granite)  varying  in  width 
from  a  fe«r  inches  to  40  or  50  feet.  In  addition  to  these  there  are  later  eruptive  rocks  of  Secondary  age,  occurring 
either  in  dikes  or  massive  bodies,  of  whose  extent  and  character  only  imperfect  data  are  obtainable.  The 
prevailing  gneiss  of  the  region  is  of  a  type  of  rock  oot  uncommon  in  other  mining  regions;  and  for  purposes  of 
description  the  name  u  granite- gneiss'"  has  been  adopted  for  this,  for  the  reason  that  it  is  largely  a  massive  rock, 
in  which  the  bedding  is -either  indistinct  or  not  at  all  visible.  At  times  this  gneiss  is  coarsely  crystalline,  at  others 
tiue-graiiiied,  in  which  case  the  proportions  of  hornblende  and  biotite  are  relatively  greater  and  the  rock  assumes  a 
darker -color.  Quartz  is  alwa\  s  prominent  in  it.  In  the  coarse  rock  two  feldspars  are  visible,  an  orthoclase  feldspar. 
generally  of  a  delicate  pink  tinge,  and  a  white  opaque  feldspar,  which  is  tricliuic,  and  frequently  shows  the 
characteristic  striataon  on  the  basal  cleavage  faces.  In  a  specimen  from  the  eastern  base  of  Sugar-loaf,  examined 
microscopically,  plagioclase  feldspar  is  largely  predominant,  and  is  of  two  varieties,  one  probably  oligoclase,  the 
other  labradorite.  Magnetite,  apatite,  and  pale  zircons  are  sparingly  present.  This  granite-gneiss  generally  forms 
rounded  hills  with  extensive  debrts  slopes,  and  presents  but  few  prominent  or  angular  outcrops. 

The  pegmatite  vein*,  or  gangue*,  as  they  are  locally  called,  are  mostly  composed  of  white  feldspar  and  quartz. 
Parts  -of  them  are  coarsely  granular  .and  contain  some  mica,  others  are  like  a  fine-grained  granite,  and  in  still  others 
these  two  textures  are  found  bearing  irregular  relations  to  each  other.  Sometimes  they  are  notmore  than  a  finger  thick, 
crossing  the  rock  in  every  direction  •without  intersecting  each  other,  and  sometimes  they  consist  entirely  of  quartz. 
Two  of  these  veins  have  strongly  marked  characteristics,  and  have  been  traced  for  a  number  of  miles  through  the 
district.  The  first,  the  Maxwell  gangue,  runs  a  little  east  of  north  from  Four-mile  creek  to  Left-hand  creek, crossing 
the  road  to  Sunshine,  tw»  miles  from  Boulder,  andis  said  to  carry  pyrites  and  some  tellurides.  The  Hoosier  gangm1. 
whicli  is  supposed  to  form  the  westenm  limit  of  th-evfcelluride  belt,  is  about  30  feet  in  width,  and  runs  through  Gold  HUl 
in  a  direction  east  of  notfth.  A  specimen  examined  in  this  belt,  is  like  fine-grained  granite  in  appearance,  though 
consisting  chiefly  of  quartz  and  feldspar,  with  "Mack  metallic  particJes  macroscopically  visible.  The  microscope 
shows  .only  quartz,  orthodase,  microdiue,  the  remnants  of  biotite  a,n4  titauite,  and  apatite  in  small  prisms.  The 
quartz  contains  fluid  inclusions  and  Ihair-like  taicrolites  of  rutile.  Tikis  carries  silver  ore  and  gray  copper.  Thej 
tellurkle  belt  includes  the  Magnolia,  Sugar-loaf, 4*old  Hill,  and  part  «f  the  Central  districts.  In  this  belt  eruptive 
rocks  are  very  rare,  but  tlve  pegmatite  veins  are  •extremely  common.  West  of  this  region  are  enormous  masses  of 
eruptive  rock,  and  tellurides  are  not  foaind. 

In  the  Caribou  district  are  rich  siK'er  ores  -carrying  from  39  to  IL^SOO  ounces  of  silver  to  the  ton.  and  in  the 
Ward  district  veins  carrying  free  gold,  with  iron  aasd  copper  pyrites,  which  have  a  general  direction  east  and  west 
while  the  others  are  more  nearly  north  and  south. 

Of  eruptive  rocks,  that  which  forms  tiie  Sugar-loaf,  a  conical  hill  between  Four-mile  and  Boulder  creeks,  is  a  fine- 
grained porphyritic  rock  of  grayish  color,  showing  in  the  hand  specimen  small  white  feldspars,  biotite,  hornblende 
and  titanite,  the  latter,  of  a  yellow  color,  being  quite  frequent.     Under  the  microscope  the  rock  shows  some  augite  and 
a  crystalline  grouudmass  containing  a  little  quartz,  but  it  is  made  up  chiefly  of  feldspaV,  in  rounded  particles,  not 
sufficiently  well  defined  for  their  determination.    A  somewhat  similar  rock  occurs  on  the  north  bank  of  Four-mile 
creek,  which  is  more  markedly  porphyritic,  its  constituents  being  larger,  and  the  large  feldspar  predominantlv 
orthoclase.    This  rock  is  evidently  a  massive  eruption  of  very  considerable  extent,  as  it  apparently  forms  a  much 
larger  hill  west  of  the  Sugar-loaf  and  large  outcrops  up  the  north  branch  of  Four-mile  creek,  nearer  to  the  Ward 
district.    In  the  saddle  immediately  east  of  the  Sugar-loaf  is  a  small  dike  of  diabase,  and  about  half  a  mile  east  is  a 
larger  one  of  the  same  rock,  the  former  a  dense  black  rock,  in  which  only  small  plagioclase  crystals  can  be 
distinguished,  the  other  a  granular  mixture  of  augite,  feldspar,  and  ore  particles.     Both  are  free  from  oliviiie. 
The  former  has  a  little  globulitie  glassy  base,  while  the  hitter  is  entirely  crystalline. 
VOL  13 5 


66  PRECIOUS  METALS. 

At  Jamestown  (also  known  as  Jimtown)  occurs  a  normal  quartz-diorite  of  rather  light  color,  although  it  contains 
considerable  hornblende.  Titanite  is  also  abundant  in  this  rock,  and  it  forms  a  dike,  running  east  and  west,  almost 
in  the  street  of  the  town.  The  cliffs,  over  500  feet  in  height  near  Jamestown,  are  formed  of  quartz-porphyry  of  a 
white  color,  which  is  partly  due  to  alteration  and  partly  to  the  absence  of  basic  minerals.  It  is  composed  of  pale 
flesh-colored  orthoclase,  sometimes  having  crystals  one  inch  in  diameter,  with  quartz,  which  is  not  particularly 
prominent,  and  occasionally  a  bleached  mica.  The  ground-mass  is  micro-crystalliue,  and  consists  almost  wholly  of 
quartz,  with  a  few  small  crystals  of  orthoclase  and  plagioclase  felds-par.  By  its  appearance  it  should  be  an  older 
rock  than  any  of  the  others.  It  contains  67  per  cent,  of  silica,  and  by  assay  no  gold. 

A  dike  is  found  in  the  Ward  district  which  contains  pyrites,  a  ,!  is  supposed  to  be  a  continuation  of  one  of 
those  in  the  Sugar-loaf  district;  but  as  no  specimens  were  obtained,  its  determination  could  not  be  made.  Still 
another  dike,  called  the  Black  Eagle,  south  of  Sugar-loaf,  is  said  to  have  been  traced  16  miles  in  an  east  and  west 
direction. 

MINES. — The  mines  of  Boulder  county  are  chiefly  noted  for  the  occurrence  of  telluricle  minerals,  next'  to  the 
native  metals  the  richest  and  rarest  ores  that  occur  in  nature. 

The  telluride  belt  occupies  the  eastern  part  of  the  district,  extending  to  within  a  short  distance  of  the  sedimentary 
beds  on  the  east.  Its  western  limit  may  be  roughly  defined  by  a  line  running  from  Jamestown  west  of  Gold  Hill  and 
through  the  Sugar-loaf.  It  comprises,  as  already  stated,  the  Magnolia,  Sugar-loaf,  Central,  and  Sunshine  districts. 
West  of  these  it  is  said  that  no  tellurides  have  been  found.  In  Caribou  district,  where  the  earliest  discovery  was 
made  in  1869-'70,  the  ores  are  mainly  argentiferous  galena,  and  are  generally  quite  rich.  In  the  Ward  district,  at  the 
head  of  Left-hand  creek,  the  ores  are  largely  pyritiferous,  and  contain,  where  decomposed,  free  gold,  but  are  generally 
difficult  of  reduction.  In  the  Saint  Vrain,  on  the  other  hand,  where  comparatively  small  developments  have  been 
made,  there  are  large  veins  rich  in  copper,  but  contain  little  silver. 

The  district  as  a  whole  is  characterized  by  exceptionally  rich  ores,  in  spite  of  which  development  has  been  very 
irregular  and  production  uncertain.  This  is  due  in  large  part  pvobably  to  the  somewhat  irregular  manner  of 
occurrence  of  the  ores.  The  veins,  which  are  popularly  regarded  as  true  fissure  veins,  and  generally  stand  at  a 
steep  angle,  are  often  of  great  width,  but  the  rich  ore,  on  the  other  hand,  is  concentrated  in  thin  streaks  and  not  very 
continuous  bodies.  If  we  confine  the  term  true  fissure  vein  to  its  narrowest  limits,  and  apply  it  only  to  that  form  of 
vein  which  was  once  evidently  a  strong,  deep-seated,  open  fissure  that  has  been  filled  in  by  vein  matter  and  ore 
foreign  and  distinct  from  the  country  rock,  there  are  probably  no  true  fissure  veins  in  this  district.  As  far  as 
known,  the  vein  material  is  almost  without  exception  an  altei-ation  of  the  country  rock,  which  is  impregnated  with 
rich  mineral.  This  impregnation  has  taken  place  either  along  the  contact  of  a  porphyry  body  with  the  country  rock 
or  in  a  pre-existing  vein  of  pegmatite,  or  again  along  some  fault  or  jointing  plane  in  the  country  rock  itself  which 
has  been  favorable  to  the  concentration  and  precipitation  of  metallic  minerals  from  their  solutions.  The  direction 
of  the  veins  is  in  general  between  northeast  and  northwest,  but  in  Ward  district  an  east  and  west  direction  seems 
to  prevail.  Their  plane,  as  already  stated,  stands  at  a  high  angle,  approaching  the  vertical. 

Placers  have  been  worked  at  various  points  in  the  narrow  valleys  which  intersect  the  districts.  Though  rich, 
their  superficial  extent  cannot  be  great,  and  no  data  have  been  gathered  in  regard  to  them. 

MINERALS. — No  exhaustive  miueralogical  study  has  yet  been  made  of  this  interesting  region.  Among  such 
rare  deposits  the  temptation  to  discover  new  species  is  great,  and  it  is  necessary  to  accept  with  caution  the  statements 
as  to  their  occurrence.  In  the  list  below  the  attempt  has  been  made  to  give  as  complete  as  possible  an  enumeration 
of  the  unusual  minerals  occurring  here  under  the  following  categories :  I.  Tellurides — «.  Old  species  proved  to 
occur,  and  cited  by  standard  works  on  mineralogy ;  b.  New  species  recognized  by  standard  works  on  mineralogy ; 
c.  New  species,  probably  good,  but  needing  further  investigation  ;  d.  Mixtures  described  as  species.  II.  Other 
minerals  mentioned  which  have  not  been  confirmed  by  publication  or  analyses.  The  occurrence  of  those  marked  with 
an  asterisk  is  doubtful  either  as  a  species  or  in  point  of  occurrence,  and  needs  further  investigation. 
I.  Tellurides — a.  Old  species  proved  in  Boulder  county: 

Altaite  (PbTe) ;  anal,  by  Genth.     (Cited  by  Dana  and  Naumauu-Zirkel). 

Hessite  (Ag2Te);  anal,  by  Geiith. 

Hessite,  auriferous=petzite.    Genth;  not  indep.  sp. 

Sylvanite  (AgTe2+ AuTe2) ;  anal,  by  Geuth.     Cited  by  D.  &  Z. 

Tellurite  (TeO2) ;  anal,  by  Genth.     Cited  by  D.  &  Z. 

Tellurium,  native,  Geuth.     Cited  by  D.  &  Z. 
b.  New  species  recognized : 

Calaverite  [M(AuTe)2+AgTe2],  sp.  by  Genth,  from  Calaveras  co.,  Cal.     Cited  by  D.  &  Z.,  sometimes 
regarded  as  a  variety  of  sylvanite. 

Coloradoite  (HgTe),  sp.  nov.  by  Genth.    Cited  by  D.  &  Z.,  orig.  from  Boulder  co. 

Schirmerite  [3(Ag2Pb)  S+2(Bi2S3)],  sp.  nov.  by  Geuth.     Cited  by  D.  Groth  and  Z.    A  mineral  of  the 
same  name  by  Endlich,  from  the  same  locality,  is  pronounced  a  mixture.     Orig.  from  Boulder  co. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  67 

c.  New  species  needing  further  investigation : 

Ferro-tellurite  (FeTeO4),  sp.  nov.  Genth.     Mentioned  by  Groth.    Orig.  from  Boulder  co. 
Magnolite  (Hg2TeO4),  sp.  nov.  by  Genth.    Orig.  from  Magnolia  district;    decomposition  product  of 
coloradoite  mentioned  by  Groth. 

d.  Mixtures  described  as  species  : 

Heuryite,  Eudlich.     Universally  pronounced  a  mixture. 

Lionite,  sp.  uov.  by  Berdell.    Considered  impure  tellurium  by  Dana  (App.  Ill,  p.  119). 

Tellnre-pyrite,  J.  A.  Smith.    Descr.  by  C.  U.  Sheppard ;  from  description,  probably  a  mixture. 

e.  Menorite  (Ni2Te3),  sp.  uov.  by  Genth.    Orig.  from  California.    No  anal.     Smith  authority  for  Boulder  co. 
II.  Other  minerals  mentioned: 

*Amalgam.    Authority,  Smith. 
Argeutite.     Authority,  Smith. 
*Bismuth,  native,  sulphide,  and  carbonate.     Smith. 
Copper,  native,  minute  crystals.     Smith. 
*Iodyrite.     Endlich. 
*Kobellite.     Smith.    Sp.  not  recognized  in  Dana. 

Mercury.     Smith. 
*Pyrargyrite.    Eudlich. 

Roscoelite.     Sp.  uov.  Genth.    Eoscoe  believes  it  a  mixture. 

CENTRAL  DISTRICT. — The  most  prominent  mine  in  this  district  is  the  Golden  Age,  near  Jamestown.  It  is  on 
the  contact  of  porphyry  with  the  Archaean,  the  former  constituting  the  hanging  wall.  The  vein  is  about  40  feet  in 
width.  The  richest  ore  conies  from  a  streak  of  white  quartz  from  1  to  2  feet  thick  on  the  foot  wall,  which  is 
sometimes  almost  a  mass  of  free  gold.  Pyrites  prevail  toward  the  hanging  wall,  but  small  rich  concentrations  of 
gold  are  also  found  at  intervals. 

GOLD  HILL  DISTRICT. — This  is  in  the  telluride  belt,  and  is  traversed  by  the  Hoosier  gangue.  Many  of  the 
telluride  veins  cross  the  Hoosier  gangue,  and  are  said  to  be  richer  in  its  neighborhood.  The  most  prominent  among 
these  are  Cold  Spring  and  Goldsmith  Maid.  The  Red  Cloud  is  the  oldest  mine  in  the  district,  and  is  the  one  in  which 
tellurides  were  first  discovered  in  1872.  Its  vein  is  3.J  feet  in  width,  and  the  ore  was  telltmdes  at  the  surface  and 
auriferous  pyrites  iu  depth.  The  Slide,  Melviua,  and  Prussian  are  also  important  deposits.  The  Emancipation  is 
near  the  Sunshine  district.  All  these  ore  in  the  granite-gneiss,  which  here  offers  but  few  good  exposures.  The 
Washington  Avenue  mine,  west  of  Gold  Hill,  carries  galena,  blende,  and  pyrites. 

SUNSHINE  DISTRICT. — This  district  comprises  the  easternmost  development  of  the  telluride  belt.  Its  ores  are 
generally  of  lower  grade,  free  gold  and  tellurides  occurring  in  the  upper  portion,  passing  into  pyritiferous  ores  in 
depth.  Prominent  mines  are  the  American,  Grand  View,  Sunshine,  Osceola,  and  Young  America. 

SUGAR  LOAF  DISTRICT. — In  this  district  the  Yellow  Pine  mine  is  an  enrichment  of  the  Hoosier  gangue  of 
pegmatitic  granite.  Other  prominent  mines  are  Baife's  lode  and  the  Emerson,  both  carrying  telluride  in  granite- 
gneiss. 

MAGNOLIA  DISTRICT. — This  is  at  present  the  southern  limit  of  the  telluride  line.  Here,  as  well  as  in  the 
neighborhood  of  Jamestown,  the  gueissic  character  of  the  country  rock  is  very  distinct,  and  the  bedding  planes  are 
easily  distinguishable.  The  prevailing  strike  seems  to  be  in  a  northeasterly  direction,  which  is  also  that  of  most 
of  the  veins  of  the  telluride  belt.  The  Senator  Hill  is  one  of  the  most  promising  mines  of  the  district.  In  the 
Keystone  and  Mountain  Lion,  which  are  said  to  be  on  the  same  vein,  a  narrow  deposit  only  from  6  to  7  inches  in 
width,  the  new  mineral  coloradoite  is  found. 

WARD  DISTRICT.— Between  Gold  Hill  and  Ward  the  gneiss  is  much  contorted  and  the  bedding  very  plain,  and 
bodies  of  eruptive  rock,  which  were  comparatively  wanting  in  the  telluride  belt,  are  here  frequent.  The  most 
important  mines  are  the  Niwot,  Columbia,  and  Stoughton.  The  ores  are  sulphides  of  iron  and  copper,  carrying 
gold,  and  therefore,  when  undecomposed,  difficult  to  reduce. 

CARIBOU  OR  GRAND  ISLAND  DISTRICT  is  situated  at  an  elevation  of  nearly  10,000  feet  above  sea-level.  Its 
most  important  mine  is  the  Caribou,  which  was  discovered  in  1869.  and  has  produced  a  very  large  amount  of  silver 
ore.  This  is  a  massive  mixture  of  galena,  chalcopyrite,  and  ziucblende,  which  occurs  in  gneiss,  but  closely  associated 
with  diabase.  Other  important  mines  are  the  No  Name  (which  is  said  to  cross  the  Caribou  and  fault  it),  the  Boulder 
County,  and  Native  Silver.  The  ores  of  this  district  are  essentially  silver-bearing,  but  also  carry  some  gold. 


68 


PRECIOUS  METALS. 


Mine. 


Country  rock  and  vein. 


Ore  and  gangnc. 


CENTRAL  DISTRICT. 

Goldeu  Age  (near  Jamestown) 
Smuggler 

GOLD  HILL  DISTRICT. 

American 


Cold  Spring 

MAGNOLIA  DISTRICT. 

Keystone 

Mountain  Lion 


WAKD  DISTRICT. 


Nelson. 
Niwot.. 


SUGAR-LOAF  DISTRICT. 

Emerson 


Yellow  Pine 

Bailo's lode 

GRAND  ISLAND  DISTRICT. 

Boulder  County ; 

Caribou .' 

Horsefall  lode 

Native  Silver  . . . 


Foot  wall  aneiss;  hanging  wall  porphyry .    Vein  vertical;  strike, 
E.  and  W. ;  dip,  44° ;  40  feet  wide. 

Mica-schist.    Strike,  N.  and  S.;  dip,  60°  E 


Granite-gneiss.    Strike,  NE. ;  dip,  84°  SE. 


No  specimens.    From  the  gangue  it  is  apparently  fine-grained 
granite,  and  a  much-altered  porphyry  is  near  by. 


Gneiss.    No  specimens.    Vein  :  dip,  65°  ;  2  feet  wide 
Gneiss.    Vein :  strike,  NE. ;  dip,  65° ;  2  feet  wide 


Decomposed  mica-schist.    Strike,  NE. ;  dip,  62°. 


Granite-gneiss  hanging  wall  and  porphyry  foot  wall.    Strike,  E. 
andW. ;  dip,  70°  N. 


Altered  gneiss 

Granite,  with  reddish  feldspars  and  but  little  mica. 


Coarse  granite-gneiss  with  red  feldspars,  in  which  are  veins  of 
fine-grained  biotite-grauite. 

Vein:  strike,  E.  and  W. ;  dip,  55°  N 


Syenitic  gneiss.    Diabase  occurs  in  the  neighborhood.    Vein : 
strike,  E.  and  W. ;  dip,  14°  N.  (76°  ?) 

Mica-schist.    No  specimen.    Strike,  E.  and  W. ;  dip,  85°  If 

A  fine-grained  biotite-granitc.     Near  the  vein  the  biotite  has  dis- 
appeared. Vein:  strike,  E.  and  W. ;  dip,  5°  N.  (85°?) 


Free  gold,  with  iron  and  copper  pyrites  and  quartz. 
Tellnrides  and  pyrites  in  siliceous  gangue  and  altered  country. 


Tellnrides  of  gold,  silver,  and  mercury,  with  free  gold,  sul- 
phide of  iron,  zinc,  lead,  and  copper;  no  specimens. 

Tellurides.  Specimen,  evidently  from  the  side  of  the  vein,  is 
attrition  material ;  clay,  rounded  pieces  of  quartz,  with  py- 
rites and  Jellurides. 

Tellnrides  in  quartz  gangue.    No  specimens. 

Iron  oxide  and  free  gold,  with  tellnrides.  Gangue :  quartz  and 
feldspar. 

Anriferons  chalcopyrite  and  pyrite  with  free  gold.  Gangue: 
quartz  and  altered  country. 

Massive  pyrite  and  chalcopyrite  cemented  by  quartz. 


The  same  rock  impregnated  with  fine  grains  of  pyrite  and  tel- 
lurides. 

Gray  copper,  azurite,  malachite,  and  some  unknown  greenish 
mineral  in  a  decomposed  gneiss  or  granite. 

At  the  contact  of  granites  is  quartz  with  a  little  galena,  pyrites, 
and  black  stains. 


Galena,  pyrite,  and  blonde  in  quartz ;  blende  crystals  covered  by  a 
layer  of  hematite. 

A  massive  mixture  of    galena,  chalcopyrite,  zincblende,  and  a 
mineral  called  "antimony". 

Chalcopyrito  and  pyrite  with  free  gold,  some  galena  and   zinc- 
blende. 

Mixture  of  galena  and  sulphides. 


JEFFERSON  COUNTY. 

This  county  includes  the  foot-hill  region  south  of  Boulder  county  as  far  as  South  Platte  river  and  a  narrow  strip 
of  the  mountain  region.  Although  mainly  a  mountain  county,  and  surrounded  by  important  mining  districts,  it 
reports  no  product  of  the  metallic  minerals.  On  the  other  hand,  its  production  of  coal  from  Ealston  creek,  Golden, 
and  Morrison,  and  of  valuable  fire-clays  and  building-stone  all  along  the  foot-hill  region,  is  extremely  important. 
From  the  basaltic  mesas  at  Golden  a  number  of  interesting  zeolitic  minerals  have  been  obtained  by  Mr.  Cross,  of  the 
United  States  geological  survey,  among  which  are  analcite,  apopliyllite,  chabazite,  laumontite,  mesolite,  natrolite, 
scolecite,  stilbite,  and  thomsonite.  Jet  is  also  found  in  the  Tertiary  beds  under  the  lava  flows  and  bole. 


GILPIN  COUNTY. 

This  is  the  smallest  county  in  the  state,  and  consists  of  a  triangular  bit  of  mountain  region,  covering  180  square 
miles  of  surface,  drained  by  the  north  fork  of  Clear  creek  and  adjoining  Jefferson  county  on  the  west.  It  is  the 
oldest  mining  region  in  the  state,  the  first  gold  being  discovered  here  in  Eussell  gulch  in  1859,  and  is  still  the 
greatest  gold  producer.  Its  placer  deposits,  lying  along  the  bottoms  of  deep  ravines,  are  of  limited  extent,  but 
they  are  extremely  rich,  and  though  most  of  them  have  been  worked  over  several  times,  they  still  yield  a  certain 
amount  of  gold. 

This  county  is  entirely  in  the  Archa3au  formation,  which  consists  mainly  of  gneiss,  the  prevailing  type  being 
structureless  granite-gneiss,  already  described  in  the  section  on  Boulder  county.  The  gneiss  is  penetrated  by 
various  bodies  of  porphyry ;  but,  owing  to  the  peculiar  readiness  with  which  the  rocks  yield  to  atmospheric  influences, 
few  characteristic  outcrops  are  found,  so  that  the  geological  structure  is  not  readily  recognized  on  the  surface. 
Here  also  the  veins  are  mainly  alterations  of  the  country  rock  along  certain  planes,  and  rarely,  if  ever,  show  the 
character  of  a  pre-existing  open  fissure  filled  by  foreign  material.  In  some  cases  the  vein  material  seems  to  be  a 
porphyry  dike.  Many  of  the  veins  have  been  traced  to  a  very  considerable  depth,  in  some  cases  to  over  1,000  feet, 
and  it  is  claimed  that  some  have  been  traced  in  length  between  2,000  and  3,000  feet.  The  direction  of  the  veins  lies 
either  between  north  and  south  and  northeast  and  southwest,  or  within  10°  of  east  and  west.  Among  the'more 
important  veins  the  Gregory  &  Briggs,  Bates,  and  a  few  others  belong  to  the  former,  the  Bobtail,  Burroughs, 
Gnnuell,  and  others  belonging  to  the  latter  group.  In  all  the  dip  is  generally  near  the  vertical.  Faulting  or 
displacement  of  the  vein  is  rare,  but  where  the  vein  material  is  porphyry  it  frequently  contains  inclosed  fragments 
of  gneissic  country  rock.  In  one  mine  rounded  boulders  of  gneiss  of  considerable  size  have  been  found  in  the  vein 
at  a  depth  of  about  700  feet  from  the  surface,  but  whether  their  form  is  due  to  attrition  of  the  two  walls  or  to  the 
rounding  action  of  water  and  mineral  solutions  is  not  known. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  69 

The  ores  are  mainly  a  mixture  of  pyrite  and  chalcopyrite,  with  less  frequently  galena  and  zincblende.  carrying 
more  or  less  gold.  In  the  northern  portion  of  the  district,  however,  galena  ores,  with  zincblende  and  pyrite,  carrying 
silver,  occur,  but  as  a  rule  contain  little  or  no  gold  ;  and  similar  deposits  almost  surround  the  extremely  circumscribed 
limits  of  the  gold-bearing  area,  whose  radius,  taking  Central  City  as  a  center,  is  only  about  1  £  miles.  In  the  gold 
veins  the  richer  ore  generally  occurs  in  streaks  that  are  not  more  than  one  foot  wide,  a  compact  fine-grained 
mass  of  pyrite,  copper  pyrite  being  as  a  rule  richer  than  the  ordinary  pyrite.  The  rest  of  the  vein,  which  often 
attains  a  width  of  many  feet,  carries  pyrites  (irregularly  disseminated  through  a  more  or  less  decomposed  mass  of 
•  country  rock)  either  in  the  form  of  white  clayey  material  or  as  a  mixture  of  quartz  and  i'eldspar.  Outside  the 
narrow  streaks  of  solid  sulplmrets,  the  bulk  of  these  ores,  as  they  are  extremely  difficult  to  smelt,  are  generally 
treated  by  mill  process,  and  the  percentage  of  loss  is  generally  much  higher  than  in  more  completely  oxidized  ores,  or 
those  which  are  free  from  pyrites,  averaging  probably  40  per  cent.  The  richer  portions  of  the  ore  and  concentrations 
of  mill  tailings  are  sent  to  the  smelting  works  in  the  valley  below.  According  to  Mr.  A.  N.  Eogers,  of  the  Bobtail 
mine,  who  has  had  long  experience  in  the  underground  workings  of  this  district,  the  veins  invariably  follow  the 
cleavage  planes  of  the  country  rock,  the  planes  crossing  the  strata  with  a  nearly  vertical  dip,  while  the  stratification 
of  the  country  rock  has  a  dip  to  the  eastward.  He  also  states  that  the  porphyry  has  its  cleavage  in  common  with  the 
country  rock  where  the  cleavage  does  not  invade  the  veins  themselves,  the  joints  or  laminae  taking  the  line  of  the 
veins  and  lying  parallel  with  their  Avails.  Hence  he  reasons  that  the  porphyry  is  older  than  the  veins,  inasmuch 
as  the  cleavage  is  older  and  intersects  the  porphyry.  These  observations  are  of  interest  as  giving  a  slight 
indication  of  the  age  of  deposits  in  the  Archoeau,  for  which,  as  a  rule,  it  is  impossible  to  obtain  any  definite  data. 

The  mountain  region,  from  12  to  15  miles  in  width  between  the  mining  districts  and  the  plains,  mainly  included  in 
Jefferson  county,  which  consists  also  of  Archrean  rocks,  has  hitherto  proved  relatively  barren  of  valuable  minerals. 
In  this  region  the  rocks  are  comparatively  unclecomposed  and  the  bedding  planes  remarkably  distinct,  having  a 
prevailing  easterly  dip.  They  are  generally  gueissic  in  character,  with  some  granite,  and,  as  a  rule,  are  highly 
siliceous.  \ 

MINERALS. — Besides  the  ordinary  sulphides  of  iron,  copper,  zinc,  and  lead,  sulphides  and  arsenides  of  silver 
are  found  ;  and  among  rarer  minerals  the  occurrence  of  enargite  (sulphide  of  copper  and  arsenic)  in  massive  crystals 
in  the  Powers  mine,  in  Eussell  district,  is  noteworthy.  From  the  Wood  mine,  in  Leavenworth  gulch,  a  small  pocket 
of  pitchblende  or  uraninite  was  obtained  by  Mr.  Eichard  Pearce,  who  first  noticed  it  in  the  refuse  of  the  dump. 
Aurichalcite  is  reported  by  Dr.  Genth  in  connection  with  zinc  minerals,  cobellite  by  Dr.  Loew,  and  melaconite  by 
Dr.  Peters  with  copper  minerals. 

The  following  minerals  are  reported  from  this  county  by  J.  Alden  Smith  and  Dr.  Endlich,  but  no  analyses  are 
given :  Allophane,  azurite,  calamine,  chalcanthite,  cerargyrite,  copper  (native),  garnet,  gold  (in  crystals),  goslarite, 
greeuockite,  jarosite,  lievrite,  maguesite,  magnetite,  magnetic  pyrite,  marcasite,  mispickel,  molybdenite,  selenium, 
siderite,  smithsouite,  sulphur  (native),  tourmaline,  willemite,  wolfeuite,  zincite,  and  a  variety  of  uranium  minerals. 

MINING  DISTRICTS. — The  mining  districts,  like  the  county,  are  extremely  small,  and  their  limits  not  definitely 
known.  The  Gregory  district  includes  the  mines  in  the  immediate  vicinity  of  Black  Hawk  and  Central,  the  most 
important  being  the  Bobtail,  which  is  the  richest  and  largest  producer,  although  worked  on  a  length  of  only 
800  feet.  On  the  Gregory  lode  claims  have  been  located  over  a  length  of  4,500  feet,  but  actual  explorations 
cover  an  extent  much  less  than  half  of  this.  It  is  expected  that  these  two  lodes,  together  with  the  Bates  (which 
lies  to  the  northwest  of  the  Gregory  and  nearly  parallel  to  it),  whose  courses  are  convergent,  will  all  unite  to  the 
southward  in  the  Mammoth  lode.  Xevada  district,  which  lies  to  the  west  of  the  Gregory,  takes  in  the  head  of 
Nevada  gulch,  and  includes  the  California,  Kansas,  Burroughs,  and  other  lodes.  The  Kussell  district  lies  to  the 
south  of  these,  in  Kussell  gulch.  The  number  of  mines  is  too  "great  to  admit  of  any  special  mention,  but  the 
folio winji  table  gives  the  data  furnished  by  specimens  collected  by  the  census  experts: 


Mine. 


Country  rock  and  remarks.  Ore  and  gangne. 


NEVAKA   DISTBICT. 


American  Flag  . 


California.. 


Hidden  Treasure  . 


Gneiss  rich  in  biotite Galena,  copper,  and  iron  pyrites,  and  some  zincblende,  cemented 

by  quartz. 

Granite-gneiss  impregnated  with  pyrite.     A  dike  of  quartz-por-     Pyrite.   ehalcopyrite.    zincblende.   and    galena,   with    siliceous 

pliyry  2  feet  tliiek  on  tbe  hanging  wall.  cement ;  in  some  portions  gray  copper. 

Same  walls  as  in  the  California  mine Chalcopyrite  and  dark  blende.    Gangne :  altered  country  rock. 

Jones Fine-grained  granite Dark  blende,  with  pyrite.  and  some  chalcopyrite.      In  one  case 

t  In  se  are  deposited  on  both  sides  of  a  thin  fragment  of  granite- 
gneiss. 

Kansas Biotite-gneiss  ;  fresh  on  foot  wall,  altered  on  hanging  wall Fiue-grained  mixture  of  pyrite,  ehalcopyrit«,  and  fahlerz. 

Bennett's  Kansas Li<;lit  granite-gneiss Fine-grained  mixture  of  pyrite  and  chalcopyrite.  with  siliceous 

cement,  associated  with  fragments  of  wall-iv 


Kent  County 


Lacrosse  (liurroughs). 
Pyrenees 


Polk  County. 


Gneiss.    On  the  hanging  wall  dark  blende  concentrated  in  the     Pyrite,  chalcopyrite,  galena,  and  dark  zincblende.  with  quartz 

fissures.  ;    •  cement. 

Fine-grained  biotite-gneiss Pyrite,  with  fragments  of  decomposed  wall-rock. 

Dark  gneiss  rich  in  biotite Massive  galena,  with  chalcopyrite  and  pyrite:  also  fragments 

of  wall-rock  cemented  by  blende  and  pyrite. 

Hanging  wall  fine  dark  mica-schist Chalcnpviite.  with  some  pyrite  cementing  frugmema  of  gneiss. 


70 


PRECIOUS  METALS. 


Mine. 

Country  rock  and  remarks. 

Ore  and  gangue. 

NEVADA  DISTRICT  —  continued. 

Fragments  of  wall-rock  with  a  little  pyrite,  or  massive  pyrito 
with  siliceous  cement. 

Pyrite  and  chalcopyrite,  with  quartz. 

Coarse  pegmatite  impregnated  with  galena,  pyrite,  and  chalco- 
pyrite. 

Chalcopyrite,  with  some  pyrite,  cemented  by  quartz. 

Quartz  and  pyrite. 
Chalcopyrite  and  pyrite  in  altered  country  rock. 
Pyrite  and  chalcopyrite  with  quartz. 
Porphyry  heavily  impregnated  with  pyrite. 

(Massive  mixture  of  pyrite,  chalcopyrite,  zincblende,  and  galena. 
t    Gangue:  altered  country. 

Pyrite  and  chalcopyrite.    Gangne  :  altered  country. 

Mixture  of  pyrite  and  fluorito;  galena  and  falilerz  occasionally 
present. 

Massive  enargite,  with  pyrite  and  fluorite. 
Enargite,  fahlerz,  and  pyrite.    Gangue:  feldspar  and  quartz. 
Pyrite.    Gangue  :  quartz  and  feldspar. 

Mixture  of  galena,  blende,  chalcopyrite,  and  occasional  ruby  sil- 
ver.    Gangue  rock  :  white  porphyry. 

Decomposed  granite,  in  which  cerussite  and  chlorides  have  been 
deposited. 

Pyrite,  with  copper  and  arsenical  pyrites  and  zincblende.  Gangue: 
quartz  and  feldspar. 

Massive  galena,  with  some  cerussite  and  zincblende.    Gangue: 
bleached  and  kaolinized  country  rock. 

Massive  chalcopyrite  and  pyrite.    Gangue:  altered  country  rock. 

Cerussite  ;  alteration  products  of  galena,  with  stains  of  copper. 
Gangue  :  altered  country  rock. 

West  Flack 

Forks                      

GREGORY  DISTRICT. 

Bobtail 

Fine-grained    compact  granite-gneiss,  partly  schistose  on  the 
foot  wall. 

Cashier 

Gneiss  

Minnie 

Felsite-porphyry  impregnated  with  pyrite,  and   carrying  frag- 
ments of  Archaean  rocks. 

Gneiss   

Smith  ) 

Wain                                            J 

EUSSKLL  DISTRICT. 

i 

ENTERPRISE  AND  MOUNTAIN- 
HOUSE  DISTRICT. 

Granite.    Altered  porphyry  occurs  at  70  feet  distance         

ILLINOIS  CENTRAL  DISTRICT. 

IIAWKEYE  DISTRICT. 

Hard  Money  

Altered  gneiss  

EUREKA  .DISTRICT. 

QUARTZ  VALLEY  DISTRICT. 

CLEAR  CREEK  COUNTY. 

Clear  Creek  county  lies  to  the  south  of  Gilpin,  and  is  considerably  larger  than  the  latter,  having  an  area  of  460 
square  miles.  It  extends  from  the  western  boundary  of  Jefferson  county  to  the  crest  of  the  Colorado  range,  and 
is,  next  to  Lake  county,  the  largest  producer  of  silver  in  the  state.  Its  mines  lie  mainly  among  the  steep  rocky  spurs 
between  the  various  tributaries  of  the  main  Clear  creek,  but  it  includes  also  the  Geneva  district  across  the  divide  on 
the  south,  at  the  head  of  the  Geneva  creek,  a  tributary  of  the  South  Platte.  Like  Gilpin  county,  this  county  lies 
in  the  Archaean  formation,  the  rocks  being  mainly  gneissic,  with  subordinate  development  of  granite.  Porphyry 
dikes  seem  much  more  frequent  than  in  Gilpin  county,  but  this  may  be  due  in  part  to  the  steepness  of  the  mountain 
slopes,  on  which  the  character  of  the  country  rock  is  more  readily  distinguished.  The  veins,  like  those  of  Gilpin 
county,  seem  to  be  mainly  alterations  of  the  country  rock  along  a  jointing  or  fan!  t- plane,  and  are  frequently  in 
direct  connection  with  the  porphyry  dikes,  which  form  either  one  of  the  walls  or  constitute  the  vein  material  itself. 
In  some  cases  also  the  vein  seems  to  be  an  impregnation  of  a  pre-existing  pegmatite  vein  in  the  gneiss. 

MINERALS. — The  ores  of  Clear  Creek  county  are  essentially  silver-bearing,  the  silver  being  derived  from 
argentiferous  galena,  and  in  part  from  fahlores.  In  the  eastern  or  lower  portion  of  the  district,  where  the  earliest 
developments  were  made,  the  ores  are,  however,  mostly  pyritiferous,  and  contain  relatively  little  galena,  hence  yield 
both  silver  and  gold.  In  the  upper  districts,  around  Georgetown,  they  are  mainly  silver-bearing.  The  rich  ores 
are  smelted  directly,  and  are  generally  sent  out  of  the  district  for  this  purpose.  A  very  considerable  proportion  of 
the  product  is,  however,  concentration  ore,  which  is  generally  an  impregnation  of  the  country  rock  at  a  greater  or 
less  distance  from  the  main  crevice.  This  impregnation  seems  to  take  place  by  preference  on  one  side  of  the  vein, 
and  this  is  generally  the  foot  wall.  These  ores  are  concentrated,  as  a  rule,  in  Georgetown,  and  the  concentrates  are 
sold  to  smelters.  A  relatively  small  proportion  of  the  oxidized  portion  of  the  deposits,  especially  those  which  are 
comparatively  free  from  lead  and  zinc,  are  suitable  for  milling.  There  is  no  doubt  that  this  district  contains  an 
unusually  large  proportion  of  valuable  veins ;  but  their  development  has  been  incommensurate  with  the  intrinsic 
value  of  the  deposits  for  various  reasons,  among  which  are  pernicious  systems  of  working  and  the  abundant  cases 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION. 


71 


of  litigation  arising  from  the  close  vicinity  of  the  veins  to  each  other  and  their  frequent  crossings.  A  very  large 
proportion  of  the  more  important  mines  were  closed  at  the  date  of  visit,  and  consequently  the  returns  obtained  by 
the  expert  are  far  from  complete.  Under  these  circumstances  it  were  useless  to  attempt  to  form  any  generalizations 
on  the  direction  or  interdependence  of  the  veins  as  a  whole. 

Besides  the  ordinary  metallic  sulphurets,  the  following  minerals  are  reported  as  occurring  in  the  county: 
Anglesite,  argentite,  azurite,  bornite,  bournonite,  calamine,  caledonite,  chrysocolla,  fahlerz,  garnet,  minium, 
proustite,  psilomelane,  pyromorphite,  silver  (native),  stephanite,  sternbergite,  stibnite,  tennantite,  tetrahedrite. 

The  following  table  gives  the  character  of  ore  and  country  rock  of  the  mines  from  which  specimens  were 
obtained : 


Mine. 


Country  rock  and  remarks. 


Ore  and  gangue. 


BANNER  DISTRICT. 

First  National... 


Big  Chief. 
Nathan . . . 


Mica-gneiss;  finely  bedded  on  hanging  wall;  iron-stained  and  schis- 
tose on  foot  wall. 

Mica-gneiss,  containing  on  the  foot  wall  a  number  of  small  pink 
garnets. 

Gneiss 


CASCADE  DISTRICT. 

Muscovite 


CORRAL    AND  TRAIL    BUN   DIS- 
TRICT. 


Donaldson . 


Brooklyn 

GENEVA  DISTRICT. 

Baltic 

GRIFFITH  DISTRICT. 


Burleigh 

Consolidated  Hercules. 

Diamond 

Dunderberg 

Equator 

Junction 

Colorado  Central 


IDAHO  DISTRICT. 
Champion 

Gem 


Idaho  tunnel. 
Victor... 


Mackey. 


MONTANA  DISTRICT. 


Free  American  . 

Murray 

Joe  Reynolds... 


HOHBIS  DISTRICT. 


Albro 

Alexander. 
Eagle 


BEATON  DISTRICT. 


Tropic. 


SPANISH  BAB  DISTRICT. 
Fairmoun  t-Shafter 


Freeland. 


Hukill 

Mayflower. 


Hanging  wall  granite-gneiss ;  foot  wall  decomposed  gneiss  and 
felsite-porphyry. 


Hanging  wall   iron-stained  gneiss;  foot  wall  grayish  compact 
felsite. 


Gneiss . 


No  specimen. 


Gneiss,  passing  on  one  side  into  granite ;  on  the  other,  into  schists 


Porphyry  and  gneiss  (a) . 


Altered  gneiss 

Indistinctly  bedded  gneiss. 


IOWA  DISTRICT. 


Hanging  wall  mainly  white  orthoclase ;  foot  wall  gneiss. 
Gneiss  indistinctly  bedded 


Gneiss  . 


No  specimen 

White  granite  whose  mica  is  altered  to  a  light  greenish  substance 
Foot  wall  mica-gneiss ;  hanging  wall  pegmatite  vein 


Quartz,  stained  reddish  and  yellow  by  iron  oxide. 

Pyrite,  chalcopyrite,  fahlerz,  and  chalcosite.  with  quartz  matrix. 
Gangne :  altered  gneiss. 

Crumbling  iron-stained   mass  with  no  recognizable  minerals; 
probably  altered  country  rock. 


Stained   breccia-like  mass,  with  no  distinct  metallic  minerals 
•visible. 


Pyrite  in  quartz ;  smelting  ore  contains  fahlerz ;  pyrite 
thoroughly  decomposed  constitutes  free-gold  ore.  Gangne: 
altered  gneiss. 

Pyrite  and  chalcopyrite  with  fahlerz.  Gangne :  quartz  and  feld- 
spar. 

Pyrite,  chalcopyrite,  blende,  fahlerz,  and  a  little  galena  in  siliceous 
'gangne ;  occasional  pink  calcite  crystals. 


Chiefly  massive  galena  and  chalcopyrite. 


Chalcopyrite  and  argentiferous  galena. 


Chalcopyrite  and  blende.    Milling  ore :  altered  country  rock  im- 
pregnated with  particles  of  pyrite. 

Arsenical  fahlerz  with  aznrite  and  malachite.     Gangne :  altered 
country  rock. 

Galena,  zincblende,  and  pyrite  deposited  on  hanging  wall  rock. 

Zincblende,  pvrite,  etc.,  altered  in  high  grade  ore  to  a  stained 
decomposed  mass.    Gangne :  altered  country  rock. 

Ore   and  gangue    specimens  both  granite-gneiss,    the    gangue 
specimen  having  more  visible  pyrite  than  the  pay  ore. 


Galena,  pyrite,  and  barite. 

Galena,  pyrite,  and  chalcopyrite.    Gangne:  altered  country  rock. 

Galena.    Gangue:  quartz  and  feldspar. 


Gneiss. 
Gneiss . 
Gneiss  . 


Gneiss  impregnated  on  foot  wall  with  pyrites. 


Pyrite,  chalcopyrite  with  some  fahlerz.  Gangne:  quartz  and 
feldspar. 

Galena,  pyrite,  chalcopyrite,  and  possibly  fahlerz.  Gangne: 
quartz  and  feldspar. 

Seems  to  be  mainly  country  rock  impregnated  with  chalcopyrite 
and  other  minerals  invisible  to  the  eye. 

Brilliant  mass  of  zincblende,  with  galena,  fahlerz.  and  pyrite ; 
concentration  ore  wall-rock  more  or  less  impregnated  with  these 
minerals  and  carrying  calcite. 

« 

Galena,  pyrito,  and  pyrolusite.  Gangne:  feldspar  in  large  in- 
dividuals. 

Fine-grained  mixture  of  pyrite  and  chalcopyrite ;  relative  rich- 
uessdependingonproportionof  latter.  Gangne:  altered  country 
rock. 

Much  decomposed  gneiss Pyrite  and  bornite  in  siliceous  gangue. 

Schistose  gneiss  of  varying  character Pyrite  and  galena,  with  some  fahlerz  and  zincblende  either  mas- 
sive or  mixed  with  siliceous  gangne.  Gangne:  altered  country 
rock. 

a  Porphyry  assays  0.033  to  0.083  ounce  of  silver  per  ton,  with  a  trace  of  gold. 


Gneiss  impregnated  with  pyrites  more  abundantly  on  the  foot 

wall. 
Gneiss  varying  in  depth  from  a  hornblendic  variety  to  a  feld- 

spathic. 


72 


PRECIOUS  METALS. 


Mine. 

Country  rock  and  remarks. 

Ore  and  gangne. 

UPPER  UNION  DISTRICT. 

Chiefly  massive  chalcopyrite. 

Massive  galena,  chalcopyrite,  and  pyrite,  with  a  little  fahlerz. 
Gangue  :  altered  country  rock. 

Rich  ore,  pyrite  in  quartz  ;  second-class  ore,  gneiss  impregnated 
with  pyrites. 

Pyrite  with  a  little  galena  in  quartz  ;  low-grade  ore,  gneiss  im- 
pregnated with  pyrites. 

Galena  and  zinchlende.    Gangue:  altered  country  rock. 

Neith 

VIRGINIA  DISTRICT. 

Lake 

TORK  DISTRICT. 

Clifford 

SUMMIT  COUNTY. 

By  the  recent  cession  of  the  lands  of  the  Ute  reservation  a  large  area  of  the  mesa  region  of  the  Colorado  plateau 
country  between  the  White  and  Grand  rivers,  extending  as  far  west  as  the  boundary  of  Utah,  has  been  added 
to  what  was  originally  a  small  mountain  county.  This  new  region,  with  the  exception  of  the  White  Eiver  plateau, 
at  the  head  of  the  White  river,  in  which  Palaeozoic  rocks,  cut  through  and  partially  covered  by  basalts,  are  exposed, 
is  mainly  covered  by  Tertiary  beds,  and  offers  little  prospect  of  metallic  wealth. 

As  originally  constituted,  the  eastern  end  of  Summit  county  adjoins  Clear  Creek  and  Park  counties,  the  crest 
of  the  Colorado  range  separating  it  from  the  former,  and  the  cross  range  connecting  this  with  the  Mosquito  range 
and  dividing  the  two  parks  from  the  latter,  and  includes  a  portion  of  the  Park  range,  consisting  of  the  northern 
end  of  the  Mosquito  range  and  the  Gore  mountains,  together  with  the  valleys  of  the  Blue  river  on  the  east  of  these 
mountains,  and  of  Eagle  river  on  the  west. 

The  high  mountain  portion  of  the  county  is  mainly  composed  of  Archaean  rocks,  but  along  the  valley  of  the  Blue 
there  are  fragmentary  beds  of  Mesozoic  and  Palaeozoic  rocks  which  have  escaped  erosion,  relics  of  a  former  connection 
of  the  Mesozoic  seas  which  filled  the  South  and  Middle  parks.  These  rest  on  the  Archaean  of  the  Park  range,  and 
are  repeated  on  its  west  side,  the  Park  range  probably  having  been  lifted  up  by  the  great  fault  movement  which  is 
so  well  denned  in  the  Mosquito  range.  Along  the  upper  portion  of  Eagle  river  there  are  Palaeozoic  beds  dipping 
north  and  resting  on  the  Archaean  of  the  northern  end  of  the  Sawatch,  which,  as  one  goes  westward  down  the  stream, 
gradually  pass  under  the  succeeding  higher  Mesozoic  beds,  and  are  finally  lost  under  the  Tertiary  of  the  lower  Grand 
and  White  rivers.  Associated  with  the  lower  beds  is  a  very  considerable  development  of  Secondary  eruptive  rocks, 
which  are  very  inadequately  represented  on  the  existing  geological  maps  of  this  region. 

The  lofty  mountain  crests  which  bound  the  county  on  the  east  have  hitherto  been  a  serious  barrier  to  the 
development  of  its  ores,  which,  though  frequently  occurring  in  large  masses,  are  on  the  average  of  low  grade,  and 
cannot  support  heavy  freight  or  reduction  charges.  The  recent  advent  into  the  valley  of  the  Blue  river  at  Frisco 
of  the  Denver  and  Rio  Grande  road  promises  to  ameliorate  this  condition  of  things  to  a  limited  extent;  but  its 
circuitous  course,  which  necessitates  the  carrying  of  freight  from  here  to  Denver  over  five  times  the  actual  distance 
in  a  straight  line,  still  involves  relatively  high  freigh:  charges  on  supplies  and  ore. 

In  this  county  there  is  a  marked  connection  between  the  prevalence  of  eruptive  rocks  of  Secondary  or  Mesozoic 
age  and  the  richness  and  magnitude  of  the  ore  deposits.  These  are  not  only  found  in  the  Archaean  and  Palaeozoic 
systems,  but  also  extend  up  as  high  as  the  Trias.  As  yet  none  of  value  are  known  to  occur  in  the  Jurassic  or 
Cretaceous  formations. 

MINING  DISTRICTS. — The  oldest  mining  districts  are  those  in  the  neighborhood  of  Montezuma  and  Peru,  near 
the  head  of  Little  Snake  river,  the  east  fork  of  the  Blue,  their  veins  belonging  to  the  same  mineral  belt  as  those 
of  Georgetown,  in  Clear  Creek  county,  and  of  Geneva  gulch  and  Hall  valley,  in  Park  county,  from  which  they  are 
respectively  separated  only  by  the  intervening  curving  crest  of  the  Colorado  range.  The  deposits  occur  in  the 
Archaean  rocks,  and  consist  mainly  of  argentiferous  galena  and  sulphurets.  Several  presumably  valuable  mines 
have  been  developed  in  the  district,  and  small  smelting  works  have  been  erected,  with  the  usual  want  of  success 
attendant  on  small  capital  and  a  limited  supply  of  ore.  No  report  was  furnished  from  this  district. 

"Numerous  ore  bodies  have  been  found  at  the  head  of  the  Blue  river,  where  the  Palaeozoic  and  Triassic  formations 
have  been  extensively  traversed  by  intrusive  sheets  of  Secondary  eruptive  rocks.  These  eruptions  have  undoubtedly 
caused  considerable  local  metamorphism  of  the  sedimentary  beds,  which  have  farther  been  extensively  dislocated 
by  a  complicated  system  of  faults,  so  that,  without  a  careful  study  in  the  field,  it  is  impossible  to  definitely  determine 
the  geological  horizon  of  any  individual  deposit.  The  principal  developments  have  taken  place  near  Breckenridge. 
on  the  northwestern  slopes  of  mounts  Hamilton  and  Guyot. 

Reports  are  at  hand  from  the  Helen  mine,  in  the  Bevan  district,  in  French  gulch,  whose  ore  body  is  an 
impregnation  of  quartzite,  called  a  vein,  striking  NNE.  and  dipping  60°  to  the  southward,  and  some  45  feet  in 
width.  The  ore  is  free  gold,  with  some  silver  in  a  quartzite,  iron-stained  by  the  leaching  out  of  the  pyrites  which  it 
originally  contained. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  73 

In  the  McKay  district  the  Naperville  mine  has  a  deposit  of  argentiferous  galena  and  carbonates  occurring 
between  an  overlying  porphyry  and  an  unreported  sedimentary  bed  below. 

The  Monte  Cristo  mine,  on  the  slope  of  Quandary  peak,  west  of  the  upper  valley  of  the  Blue,  is  a  deposit  of 
low-grade  galena,  with  some  zincblende  impregnating  the  Cambrian  quartzite.  This  deposit  is  exceptionally 
favorably  situated  for  mining,  the  quartzite  bed  in  which  it  occurs  dipping  eastward  at  the  same  angle  as  the 
spur  of  the  mountain,  and  the  overlying  white  limestone  and  succeeding  rocks  above  having  been  eroded  off  so 
that  it  forms  the  actual  surface  of  the  hill  and  can  be  quarried  out.  In  spite  of  its  low  tenor  in  silver,  said  to 
average  15  ounces  to  the  ton,  it  seems  that  under  proper  management  the  mine  ought  to  be  made  to  pay.  Veins 
have  been  discovered  at  many  points  in  the  Archaean  rocks  that  form  the  sharp  crest  of  the  Mosquito  range,  often 
in  the  most  inaccessible  localities ;  but  during  the  census  year,  so  far  as  could  be  discovered,  none  were  in  the 
condition  of  producing  mines. 

Ten-mile  district,  between  the  heads  of  Ten-mile  creek,  a  fork  of  the  Blue  nver,and  of  Eagle  river,  is  at  present 
the  most  important  mining  region  of  the  county.  The  ores  occur  mainly  in  the  Upper  Carboniferous  limestones 
and  in  the  sandstone  beds  immediately  above  them.  These  lie  at  the  western  foot  of  the  Archa3an  mass  which  forms 
the  sharp,  jagged  crest  of  the  Mosquito  range,  and  which  has  been  lifted  tip  by  the  movement  of  the  great  Mosquito 
fault.  An  area  here  of  some  10  miles  square  has  been  the  scene  of  most  wonderful  eruptive  activity  during  or  at 
the  close  of  the  Mesozoic  epoch.  In  number  and  size  the  intrusive  bodies  of  porphyry  and  porphyrite  which  occur 
in  these  sedimentary  formations,  either  as  iuterbedded  sheets,  as  dikes,  or  as  intermediate  irregularly  transverse 
bodies,  exceed  even  those  of  the  neighboring  region  of  Leadville.  Between  these  two  districts,  but  nearer  that  of 
Ten-mile,  occurs  a  Tertiary  eruptive  mass  of  the  rather  uncommon  rock  nevadite,  or  crystalline  rhyolite.  Although 
but  a  portion  of  the  probable  ore-bearing  area  has  yet  been  prospected,  the  quantity  of  metallic  minerals  found  here 
is  remarkable.  Unfortunately  for  the  prosperity  of  the  district  their  quality  is  not  so  satisfactory,  as  they  mostly 
run  very  low  in  silver  and  are  extremely  refractory,  consisting  mainly  of  pyrites,  with  a  very  considerable  admixture 
of  zincblende.  The  ore  deposits  mostly  occur  in  the  thin  beds  of  limestone,  which  are  prevalent  in  this  formation, 
at  or  near  their  contact  with  an  overlying  micaceous  sandstone.  Less  frequently  they  are  found  in  actual  contact 
with  an  intrusive  bed  of  porphyry,  and  at  other  times  impregnating  a  dike  of  porphyry  which  traverses  the 
sedimentary  formations. 

The  most  important  and  the  typical  mine  of  the  district  is  the  Robinson.  Its  ore  is  an  argentiferous  galena 
of  exceptionally  high  grade,  associated  with  pyrites  and  some  zincblende.  It  occurs  at  or  near  the  surface  of  a  bed 
of  bluish-gray  limestone,  overlaid  by  a  white  micaceous  limestone,  dipping  northward  at  an  angle  of  about  17°. 
The  ore  seems  to  be  an  actual  replacement  of  the  country  rock.  The  upper  layer,  locally  called  "  white  iron", 
which  is  a  mixture  of  fine-grained  crumbling  pyrites  with  white  mica,  nearly  free  from  galena,  seems  to  be  a 
replacement  of  a  portion  of  the  overlying  sandstone,  and  is  practically  worthless.  Below  this  the  ore  consists 
of  a  varying  mixture  of  galena  and  pyrites,  exteading  at  irregular  depths-  into  the  limestone,  and  in  the  larger 
bodies  occupying  nearly  its  whole  thickness.  The  ore  chute,  whose  maximum  width  is  100  feet,  has  been  traced 
over  a  linear  extent  of  1,000  feet,  following  the  general  direction  of  the  dip.  A  line  of  fracture,  probably  a 
fault-plane,  may  be  observed  in  the  roof  following  the  line  of  the  ore  body,  i.  e.,  a  vertical  plane  at  right  angles 
to  the  line  of  strike.  It  seems  probable  that  this  fault-plane  furnished  the  channel  through  which  the  ore  solutions 
reached  the  limestone,  inasmuch  as  pyrites  extend  apparently  into  the  fissure  as  far  as  it  has  been  opened,  and  in 
the  portions  of  the  limestone  adjoining  there  is  no  mineral  matter  at  its  contact  with  the  overlying  sandstone 
at  a  little  distance  from  the  ore  body.  Small  bodies  of  mineral  have  also  been  found  in  the  limestone  along  the 
line  of  several  minor  fault-planes,  which  are  also  at  right  angles  to  the  line  of  strike,  and  whose  displacement 
amounts  at  most  to  a  few  feet.  The  Wheel  of  Fortune,  on  the  summit  of  Sheep  mountain,  at  the  foot  of  which  the 
Eobinson  mine  stands,  has  an  extremely  rich  body  of  silver  ore  in  the  same  or  an  adjacent  .limestone  stratum  and 
adjoining  an  irregular  transverse  body  of  white  porphyry. 

On  Elk  mountain  ore  occurs  over  a  very  large  area  in  a  thin  bed  of  limestone  at  a  higher  horizon  than  that  of  the 
Eobinson.  This  ore  is  a  similar  mixtureof  pyrites  and  galena,  oxidized  near  the  surface,  andsometimes  to  considerable 
depths  along  certain  lines,  with  unaltered  sulphurets  on  either  side.  This  almost  continuous  body  has  been  developed 
by  the  adjoining  claims  of  the  White  Quail,  Aftermath,  Milo,  Badger,  Raven,  Eagle,  and  Colonel  Sellers  to  an  extent 
of  over  2,000  feet  along  the  strike  and  700  to  800  feet  on  the  dip.  While  a  great  portion  of  this  immense  mass  is 
too  poor  in  silver  to  pay  for  working,  as  an  instance  of  widely  extended  ore  deposition  it  is  certainly  remarkable. 
Where  the  same  bed  crosses  the  north  end  of  Sheep  mountain,  a  mile  or  two  to  the  eastward,  beyond  an  intervening 
gulch,  similar  great  bodies  of  pyritiferous  ores,  with  more  or  less  argentiferous  galena,  are  found  in  the  Snowbank, 
Xettie  B.,  Triangle,  and  other  mines. 

Ore  is  found  following  the  limestone  horizons  at  higher  levels  and  extending  probably  up  into  the  Triassic 
formation.  In  one  portion  of  the  district,  called  Copper  mountain,  copper  minerals  a»e  associated  to  some  extent 
with  the  iron  pyrites. 

The  Pride  of  the  West,  on  Jacque  mountain,  is  a  type  of  the  deposits  which  follow  a  narrow  dike  of  porphyry. 
Here  the  vein  mass,  which  is  from  6  to  30  feet  in  thickness,  crosses  the  formation  diagonally  and  stands 
nearly  vertical.  It  is  an  iron-stained  quartzose  mass,  through  which  run  seams  or  veins  of  barite  parallel  with  the 


74  PRECIOUS  METALS. 

walls,  one  being  particularly  persistent,  and  in  connection  with  which  the  richest  mineral  is  found.  Where  the 
siliceous  gangue  material  is  sufficiently  unaltered  it  is  found  to  be  a  decomposed  quartz-porphyry.  Another 
example  of  the  type  is  the  Little  Chicago,  which  follows  a  dike  of  decomposed  porphyry.  This  vein  or  dike  yields 
an  abundant  supply  of  water,  which  is  milky,  from  suspended  particles  of  kaolin.  Small  jets  of  water  from  the 
adjoining  rock  also  deposit  hydrated  oxide  of  iron,  but  the  bodies  of  mineral  as  yet  developed  have  been  small 
and  at  widely  separated  intervals. 

On  Eagle  river,  in  the  neighborhood  of  Bed  Cliff,  deposits  of  argentiferous  galena  and  cerussite,  associated 
with  iron  oxides.,  are  also  found  in  limestone,  sometimes  between  it  and  an  overlying  white  porphyry,  and  again 
with  a  limestone  hanging  wall  and  a  quartzite  foot  wall.  These  limestone  beds  belong  to  the  Paleozoic  system, 
and  are  probably  Carboniferous  in  age;  but  whether,  like  those  of  Ten-mile,  they  are  in  the  upper  portion  of  the 
Carboniferous,  or,  like  those  of  Leadville,  in  the  lower,  is  not  known,  nor  is  it  of  any  practical  importance.  They 
are  said  to  be  very  much  broken  and  faulted.  This  district,  as  well  as  that  of  Ten-mile,  is  now  reached  by  the 
Denver  and  Bio  Grande  railroad,  and  its  ores  are  treated  at  Leadville  or  by  some  of  the  smelters  on  the  plains. 

PARK  COUNTY. 

Park  county  embraces  the  broad  mountain  valley  of  the  South  park,  its  boundary  running  along  the  crest  of  the 
Mosquito  range  on  the  west,  and  of  the  irregular  chain  which  separates  it  from  the  Middle  park  on  the  northwest. 
It  includes  also,  on  the  northeast,  a  portion  of  the  Colorado  range  lying  to  the  south  of  Clear  Creek  and  to  the 
west  of  Jefferson  county.  The  valley  plains  are  covered  by  sedimentary  deposits  of  Mesozoic  age,  which,  with 
underlying  and  conformable  Palfeozoic  formations,  slope  up  to  the  crest  of  the  Mosquito  range  on  the  west,  but  are  cut 
off  abruptly  against  the  Archaean  on  the  east,  probably  by  a  fault.  The  coal  beds  of  the  Upper  Cretaceous  are  thus 
included  in  this  area,  and  have  been  extensively  developed  in  the  neighborhood  of  Como.  Near  Hamilton  there  are 
deposits  of  hematite  iron  ore,  whose  exact  geological  horizon  is  not  known,  and  which  have  been  but  irregularly 
developed.  Besides  the  less  precious  minerals,  there  are  salt  springs  in  the  southern  portion  of  the  park,  from  which 
at  one  time  rock-salt  was  obtained,  and  which  probably  originated  in  deposits  of  this  mineral  in  the  Triassic 
rocks.  There  are  also  indications  of  copper  in  the  sandstones  of  the  Trias,  in  the  form,  usual  in  these  strata,  of 
impregnations  of  carbonate  of  copper  accompanying  plant  remains.  As  yet  none  have  been  discovered  of  economic 
value.  Minerals  carrying  the  precious  metals  have  thus  far  been  developed  only  in  the  Palaeozoic  formations,  with 
their  accompanying  porphyries  of  Mesozoic  age,  and  in  the  underlying  Archaean. 

In  the  northeastern  corner  of  the  county  are  the  Hall  Valley  and  the  Geneva  districts,  whose  deposits  properly 
form  part  of  the  Clear  Creek  belt  of  silver-bearing  ores  and  occur  in  the  same  gneissic  formation.  The  Whale 
lode,  in  the  latter  district,  is  one  of  the  most  characteristic.  The  country  rock  is  here  a  fine-grained  gneiss,  with  a 
general  strike  of  north  and  south  and  a  steep  dip  to  the  west.  It  is  intersected  by  numerous  veins  of  pegmatite 
composed  largely  of  feldspar.  The  lode  itself  runs  northeast  and  southwest,  dipping  to  the  northwest  at  an  angle 
of  65°,  and  is  a  thin  vein,  consisting  mostly  of  barite,  carrying  also  fluorite  and  quartz,  with  irregular  bunches  of 
galena  and  gray  copper,  and  often  separated  from  the  adjoining  portions  of  the  lode  by  a  clay  gouge.  This  vein 
varies  from  an  inch  to  3  feet  in  thickness.  The  crevice  of  the  lode  is  between  5  and  10  feet  in  width,  and  outside 
the  above-mentioned  vein  consists  of  altered  gneiss,  more  or  less  impregnated  with  pyrite,  galena,  zincbleude, 
and  a  decomposition  product.  The  pyrite  is  said  to  be  confined  to  the  decomposed  wall-rock,  and  seldom  occurs  in 
the  vein  proper.  There  are  numerous  other  veins  in  the  vicinity  of  this  lode  which  are  also  characterized  by  the 
occurrence  of  barite  as  gangue  material.  The  Treasure  Vault  is  said  to  have  produced  bismuth-silver  ore. 

The  principal  mineral  developments  of  the  county  have  taken  place  along  the  eastern  slopes  of  the  Mosquito 
range,  and  have  been  mainly  derived  from  Palaeozoic  rocks,  since,  although  numerous  small  deposits  of  gold  and 
silver  have  been  found  in  the  underlying  Archaean,  which  is  exposed  near  the  crest  of  the  range  and  in  the  deeper 
canons,  and  many  interesting  minerals  have  been  obtained  from  them,  no  ore  deposits  of  considerable  value  have 
yet  been  found  in  this  formation. 

The  Palaeozoic  system  here  consists  of  the  following  series,  commencing  at  the  bottom: 

Feet. 

Cambrian  quartzite .- 200 

Silurian  or  White  limestone 200 

Lower  Carboniferous  or  Blue  limestone 200 

Middle  Carboniferous  or  Weber  grits 2, 000  to  2, 500 

Upper  Carboniferous,  consisting  of  limestones,  sandstones,  and  conglomerates 1,000  to  1,500 

These  formations,  as  well  as  the  underlying  Archaean,  have  been  traversed  by  eruptive  rocks  of  Secondary 
age,  mainly  quartz-porphyries  and  porphyrites,  which,  in  the  Archaean,  occur  generally  in  the  form  of  irregular  dikes, 
but  in  the  Palaeozoic  system  are  mainly  spread  out  in  intrusive  sheets  between  the  beds.  There  is  a  marked  connection 
between  the  prevalence  of  these  eruptive  masses  and  the  development  of  mineral  deposits.  Indeed,  in  many  cases 
here,  as  in  the  Leadville  region,  it  is  evident  that  the  ore  bodies  are  a  concentration  of  the  metallic  minerals  originally 
disseminated  through  the  masses  of  these  bodies  and  now  deposited  along  their  plane  of  contact  with  the  sedimentary 
beds,  and  extending  more  or  less  into  the  mass  of  the  latter.  The  type  of  these  deposits  may  be  found  in  mounts  Lincoln 
and  Bross,  where  most  valuable  and  extensive  ore  bodies  have  been  developed  in  the  Moose,  Bussia,  Hiawatha,  and 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  75 

other  iiiiiies,  which  enjoy  the  further  distinction  of  being  the  most  elevated  mines  in  the  country,  their  altitude 
varying  from  13,000  to  14,000  feet.  The  ores  are  mainly  argentiferous  galena  and  its  products  of  decomposition, 
carbonate  and  sulphate  of  lead  and  chloride  of  silver.  Barite  is  a  frequent  gangue  material  in  the  richest  portion  of 
the  deposit.  Pyrite  also  occurs  with  the  ore,  but  is  generally  decomposed  and  changed  to  a  hydrated  oxide, 
associated  with  more  or  less  oxide  of  manganese.  These  give  to  the  mass  of  the  ore,  which  frequently  contains 
considerable  mechanical  admixture  of  clay,  a  red  or  yellow,  or,  where  manganese  predominates,  a  black  color..  The 
deposits  occur  in  irregular  bodies,  often  of  great  size,  in  the  blue  limestone,  and  generally  near  its  upper  surface.  This 
blue  limestone  now  forms  the  surface  of  the  spurs  of  the  mountain,  sloping  east  at  an  angle  of  from  10°  to  15°,  but  was 
origiually  covered  by  a  sheet  of  quartz-porphyry,  portions  of  which  still  remain  on  the  highest  parts  of  the  peak. 
This  quartz-porphyry,  to  which  the  local  name  of  Lincoln  porphyry  has  been  given,  is  of  a  type  so  widespread 
throughout  Colorado,  and  seems  to  be  so  intimately  connected  with  the  rich  mineral  deposits,  that  it  is  worthy  of 
a  detailed  description.  It  is  so  thoroughly  crystalline  that  it  is  often  mistaken  for  granite.  Its  most  striking, 
although  not  absolutely  essential  characteristic,  is  the  occurrence  of  large  porphyritic  crystals  of  orthoclase  Of  rather 
glassy  appearance,  with  extremely  well-defined  faces,  either  in  single  crystals  or  Carlsbad  twins,  in  size  from  a  half 
inch  to  2  inches  in  length.  The  ground  mass  is  a  crystalline  mixture  of  two  feldspars,  in  which  plagioclase  sometimes 
predominates,  with  mica  or  hornblende  generally  somewhat  decomposed,  and  frequently  a  large  amount  of  free 
quartz  in  double-pointed  hexagonal  pyramids,  which  often  have  the  appearance  of  rouuded  grains.  The  quartz 
often  has  a  pink  tinge.  The  rock  itself,  taken  comparatively  fresh,  is  of  greenish-gray  color,  but  often  bleached 
by  decomposition  or  weathering.  As  to  the  age  of  the  porphyry  in  this  region,  it  can  only  be  said  that  it  is  later 
than  the  Trias ;  but  what  is  apparently  the  same  rock  is  found  in  the  Gunnison  region,  and  between  the  Xorth  and 
Middle  parks,  breaking  through  the  Cretaceous  strata.  It  is,  however,  distinctly  older  than,  and  of  a  different 
character  from,  the  Tertiary  eruptive  rocks. 

The  Dolly  Varden  mine  of  Mount  Bross  is  a  similar  deposit  of  slightly  different  type.  Its  ore,  which  is 
mineralogically  similar,  occurs  in  the  mass  of  the  limestone  in  close  proximity  to  a  vertical  dike  of  white 
quartz  porphyry.  The  dolomitic  limestone  in  which  it  occurs  is  the  same  as  that  in  which  the  previously  described 
deposits  are  found :  and  the  ore  has  been  traced  to  a  vertical  depth  of  over  100  feet,  and  in  bodies  extending  from 
40  to  50  feet  on  one  side  of  the  dike  in  the  mass  of  the  limestone.  On  Loveland  hill,  a  spur  next  south  of  mounts 
Bross  and  Lincoln,  are  numerous  deposits  in  the  same  blue  dolomitic  limestone,  the  best  known  of  which  is  the 
Fanny  Barrett,  whose  ore  body  stands  vertically  or  at  right  angles  to  the  stratification  planes,  and  is  probably 
deposited  along  a  cross  fissure  or  jointing  plane. 

In  Buckskin  gulch,  between  these  two  mountain  masses,  is  the  oldest  mine  of  the  district,  the  Phillips,  which 
is  an  immense  mass  of  .auriferous  pyrites,  also  carryuig  some  silver,  deposited  in  the  beds  of  the  Cambrian  quartzite 
near  a  dike  of  quartz-porphyry.  The  Criterion  mine,  on  the  north  wall  of  the  gulch,  is  also  in  the  Cambrian 
quartzite — an  immense  body  of  thoroughly  oxidized  material,  whose  original  character  cannot  be  determined,  but 
which  was  probably  a  varying  mixture  of  galena  and  pyrites,  carrying  both  silver  and  gold.  A  porphyrite  dike 
occurs  near  by.  Colorado  Springs  mine,  in  the  Bed  amphitheater  on  the  southwest  face  of  Mount  Bross,  is  a  rich 
deposit  of  galena  along  the  bedding-planes  of  the  white  limestone.  Here  both  diorite  and  quartz-porphyry  are- 
found  traversing  the  sedimentary  beds.  The  Sweet  Home  mine,  near  thison  the  cliff  face,  in  the  underlying  Archaean, 
is  principally  interesting  from  the  minerals  which  it  has  produced — combinations  of  silver  with  arsenic  and  antimony. 
From  the  Tanner  Boy,  also  in  the  Archaean,  on  the  opposite  side  of  the  gulch,  beautiful  rhombic  crystals  of 
rhodochrosite  are  obtained. 

In  Mosquito  gulch,  the  Orphan  Boy,  once  an  important  mine,  is  in  quartzite  underlying  the  limestone 
bed.  The  London  mine,  on  London  mountain,  at  the  head  of  Mosquito  gulch,  has  developed  two  strong  veins 
of  sulphurets,  carrying  both  gold  and  silver,  the  one  with  a  gangue  of  quartz,  the  other  of  calcite,  which  occur 
either  in  the  Blue  or  White  limestone  in  connection  with  an  intrusive  bed  of  White  porphyry.  These  veins  stand  in 
an  almost  vertical  position,  as  the  beds  in  which  they  occur  are  turned  up  at  a  steep  angle  against  the  London 
fault,  which  crosses  the  formation  diagonally,  and  by  whose  movement  the  Archaean  rocks,  which  form  the  eastern 
half  of  London  mountain,  are  brought  up  into  juxtaposition  with  the  Silurian  and  Carboniferous  beds  on  its  western 
point. 

Southward  the  masses  of  intrusive  porphyry  diminish  in  extent,  as  do  also  the  number  of  developed  mineral 
deposits.  Between  Horseshoe  and  Sacramento  gulches  rich  bodies  of  galena  and  carbonate  ore,  carrying  silver,  have 
been  developed  in  the  Sacramento  mine,  also  in  the  Blue  limestone,  to  the  east  of  the  London  fault,  from  whose 
surface  the  original  covering  of  quartz  porphyry  has  been  denuded.  On  the  west  of  the  London  fault  the 
Peerless  and  Badger  mines,  the  former  at  the  very  crest  of  the  range,  find  their  ore  in  the  same  limestone  which 
here  was  covered  by  the  White  or  Leadville  porphyry. 

PLACER  DEPOSITS. — The  mountain  masses  bordering  the  South  park  on  the  north  and  west  have,  owing  to 
the  great  elevation,  been  exceptionally  exposed  to  glacial  action.  An  enormous  amount  of  detrital  material  has  in 
consequence  been  accumulated  in  the  valleys  radiating  out  from  them,  which,  when  rearranged  and  concentrated, 
forms  valuable  placer  deposits.  The  first  placer  gold  was  discovered  in  Tarryall  creek  in  the  fall  of  1859,  and  placer 
mining  has  been  carried  on  since  that  time  with  more  or  less  vigor  in  the  valleys  of  the  Tarryall  and  of  the  Platte. 


76  PRECIOUS  METALS. 

Near  the  town  of  Fairplay  the  banks  of  the  Platte  expose  a  thickness  of  over  50  feet  of  gravel,  which  has  been 
extensively  worked  over  by  sluice  raining,  but  is  now  abandoned.  At  present,  active  work  is  confined  to  the  valley 
of  the  Platte  opposite  Alma,  where  hydraulic  working  is  carried  on  and  a  gravel  bed  of  over  60  feet  in  thickness 
on  the  east  bank  of  the  creek  is  being  developed.  Two  important  conditions  for  hydraulic  mining  on  a  large  scale 
are  present  in  the  county :  first,  an  enormous  amount  of  gravel,  and  second,  an  abundance  of  water.  It  only  remains 
to  be  practically  proved  whether  these  accumulations  of  gravel  are  sufficiently  rich  to  pay  for  working. 

LAKE  COUNTY. 

Lake  county  is  of  small  area,  having  only  450  square  miles  of  surface,  and  occupying  only  about  20  miles  of  the 
upper  valley  of  the  Arkansas,  its  boundary  following  the  crest  of  the  bordering  ranges.  Since  the  discovery  of  the 
Leadville  mines  it- has  become  second  only  to  Arapahoe  county  in  population,  and  furnishes  three-fourths  of  the  precious- 
metal  product  of  the  state.  Its  western  boundary  is  the  Sawatch  range,  which  is  an  Archa3an  nrnss  in  which  granite 
predominates  over  gneiss,  and  which  abounds  in  dikes  of  porphyry.  The  western  slopes  of  Mosquito  range  on  the 
east,  and  the  hills  on  the  north  which  form  the  water-shed  between  the  Arkansas  and  Grand  rivers,  have  a  basis 
of  Archaean  granite  and  gneiss,  more  or  less  covered  by  remnants  of  the  Palaeozoic  formations,  already  described  in 
Park  county,  which  have  escaped  erosion ;  and  their  lower  position  relative  to  corresponding  beds  on  the  eastern  side 
of  the  Mosquito  range  is  due  in  part  to  faulting  and  in  part  to  flexure  of  the  beds.  Within  these  Palaeozoic 
formations  there  is  an  enormous  development  of  eruptive  rocks,  partly  occurring  as  irregular  dikes,  but  in  the  main  as 
immense  intrusive  sheets,  following  the  bedding-planes  of  the  sedimentary  rocks.  Glacial  erosion  here,  as  in  other 
elevated  districts,  has  played  an  important  part  in  the  carving  of  the  present  mountain  outlines,  and  in  the  flood 
period  following  the  first  cold  maximum  of  the  Glacial  epoch  a  lake  was  formed,  which  occupied  the  head  of  the 
Arkansas  valley,  and  was  probably  almost  entirely  included  within  the  present  boundaries  of  the  county.  The 
stratified  gravel  and  sand  beds  which  were  deposited  at  the  bottom  of  this  lake  now  form  terrace-like  ridges  bordering 
the  present  alluvial  bottom  of  the  Arkansas  river.  Whether  the  gold  contents  of  these  gravel  beds,  like  those  of 
California  which  may  have  had  a  similar  origin,  will  be  found  to  be,  in  any  portion  of  them,  sufficiently  concentrated 
to  be  worked  at  a  profit  is  a  question  which  no  steps  have  yet  been  taken  to  solve.  The  gravels  resulting  from  the 
carving  by  erosion  of  the  later-formed  gulches  have,  however,  been  found  to  contain  paying  quantities  of  gold ;  and 
it  was  to  the  exceptional  richness  of  those  of  California  gulch,  discovered  in  the  spring  of  1860,  that  the  development 
of  the  enormous  silver  wealth  of  the  Leadville  region  is  indirectly  due.  Of  late  years  the  prominence  given  to  silver 
mining  has  diverted  attention  from  the  gravel  deposits,  and  their  development  has  been  practically  stopped.  It  is 
probable,  however,  that  a  profitable  field  for  hydraulic  mining  will  be  found  in  this  county. 

The  mineral  product  of  the  county  is  mainly  confined  to  tte  California  mining  district  or  the  mines  immediately 
adjoining  Leadville,  those  of  the  outlying  districts  furnishing  out  a  small  fraction  of  the  aggregate  product.  The 
ores  are  mainly  argentiferous  galena  associated  with  zincblende,  and,  exceptionally,  a  little  copper.  They  are 
essentially  smelting  ores,  and  their  value  is  greatly  enhanced  by  the  fact  that  thus  far  they  have  been  found  in  an 
oxidized  condition,  the  lead  occurring  as  carbonate,  the  silver  as  chloride,  in  a  clayey  or  siliceous  mass  of  hydrated 
oxides  of  iron  and  manganese.  Here,  even  to  a  greater  degree  than  in  Park  county,  the  main  body  of  the  ore  is 
confined  to  the  horizon  of  the  Blue  or  Lower  Carboniferous  limestone,  which  is  here  invariably  covered  by  an 
intrusive  sheet  of  White  or  Leadville  porphyry.  The  ore  was  at  first  supposed  to  be  confined  to  the  immediate 
contact  of  the  limestone  with  the  porphyry;  but  as  developments  have  proceeded  it  has  also  been  found  to  extend 
into  the  body  of  limestone  sometimes  to  a  depth  of  over  100  feet  from  its  upper  surface,  and  in  such  cases  in  large 
but  very  irregular  deposits,  as  is  characteristic  of  ore  masses  occurring  in  this  rock. 

Less  important  ore  bodies,  generally  carrying  gold  rather  than  silver,  are  found  at  other  horizons,  either 
along  bedding-planes  or  in  gash  veins  crossing  the  stratification.  Such  are  the  Colorado  Prince  and  Miner  Boy, 
in  the  Cambrian  or  lower  quartzite,  and  the  Green  Mountain,  Tiger,  and  Ontario,  in  the  Weber  grits,  or  Middle 
Carboniferous.  The  first  mine  opened  in  the  district,  and  the  one  which  has  produced  the  largest  amount  of  gold, 
is  the  Printer  Boy,  which  is  a  deposit  of  free  gold  with  carbonate  of  lead  and  galena,  passing  in  depth  into  auriferous 
copper  and  iron  pyrites,  which  occurs  in  a  body  of  quartz-porphyry  along  a  vertical  plane  or  pair  of  planes 
nearly  parallel,  either  as  cross-joints  or  fault-planes.  The  gangue  material  is  simply  a  white  clayey  mass  resulting 
from  the  decomposition  of  the  porphyry  itself,  and,  although  at  times  exceptionally  rich,  the  ore  seldom  shows  any 
visible  metallic  minerals.  The  Palasozoic  formations  and  accompanying  intrusive  beds  of  porphyry  have  been 
compressed  into  gentle  folds  and  broken  by  a  series  of  faults  having  a  general  north  and  south  direction  whose 
movement  of  uplift  is  as  a  rule  to  the  east.  The  prevailing  eruptive  rock  is  the  White  or  Leadville  porphyry,  which 
generally  occurs  above  the  Blue  limestone,  but  is  also  in  places  found  below  it  and  at  other  horizons.  Besides  these 
there  are  other  intrusive  sheets  of  different  varieties  of. quartz-porphyry,  generally  of  extremely  local  development. 
Along  the  western  end  or  lower  portion  of  the  spurs  of  the  Mosquito  range  on  which  the  mines  are  situated  the.actual 
surface  of  the  ground  is  very  largely  buried  to  a  depth  of  100  feet  or  more  beneath  an  accumulation  of  rearranged 
glacial  or  moraine  material,  locally  called  icash.  The  extremely  complicated  conditions  resulting  from  this  state  of 
things  renders  it  impracticable  within  the  limits  of  the  present  sketch  to  give  any  detailed  description  of  the  geological 
structure  of  the  district,  and  the  reader  is  referred  for  this  purpose  to  the  memoir  of  the  writer  on  "The  Geology 
and  Mining  Industry  of  Leadville". 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  77 

The  most  important  groups  of  mines  of  the  normal  Leadville  type,  taken  in  the  order  of  their  development  and 
of  their  relative  distance  from  the  valley,  are  as  follows  :  (1.)  Those  of  Fryer  hill,  which  is  the  western  extremity  of  a 
spur  adjoining  Evans  gulch  on  the  south,  including  the  Chrysolite,  Little  Pittsburg,  Little  Chief,  Amie,  Climax, 
Dunkin,  Matchless,  and  Lee  mines.  In  these  mines  the  ore  bodies,  which  reach  a  maximum  thickness  of  90  feet,  lie  in 
an  approximately  horizontal  position,  and  are  included  between  two  sheets  of  White  porphyry.  In  some  cases  these 
ore  bodies  are  split  up  by  the  porphyry  into  two  or  more  distinct  bodies.  They  are  distinguished  from  the  deposits 
in  other  portions  of  the  district  by  the  almost  entire  absence  of  the  original  limestone,  of  which  they  are  a 
replacement.  (2.)  The  mines  of  Carbonate  hill,  which  adjoins  California  gulch  on  the  north,  include  the  Carbonate, 
Yankee  Doodle,  Crescent,  Catalpa,  Evening  Star,  Morning  Star,  Henrietta,  .JDtna,  and  Peudery.  Of  these  the 
seven  first-named  follow  the  contact  of  the  limestone  and  the  overlying  porphyry  on  its  dip  into  the  hill  at  an  angle 
of  from  15  to  25  degrees,  and  are  east  of  Carbonate  fault,  which  runs  across  the  face  of  the  hill,  while  the  last  two 
find  the  limestone  at  a  lower  level  on  the  west  side  of  the  fault.  (3.)  To  the  west  of  Carbonate  hill  a  second  shoulder 
of  the  spur  is  Iron  hill,  which  has  been  elevated  to  its  relatively  higher  position  by  the  movement  of  the  Iron  fault, 
which,  like  that  of  Carbonate  hill,  runs  along  its  western  base.  Here  the  principal  mines  are  those  belonging  to 
the  Iron  Silver  Mining  Company,  which  with  the  Smuggler,  and,  south  of  California  gulch,  the  Eock  and  Dome, 
find  their  ore  at  or  near  the  surface  of  the  easterly  dipping  limestone,  while  the  ore  of  the  Silver  Wave  and  Silver 
Cord,  also  on  Iron  hill,  and  of  the  La  Plata,  in  California  gulch,  is  mainly  found  in  approximately  vertical  but 
extremely  irregular  bodies  extending  down  into  the  mass  of  the  limestone.  Other^important  mines  of  this  type  are 
(4)  the  Florence  group,  on  Printer  Boy  hill,  north  of  Iowa  gulch ;  (5)  the  Long  &  Derry  group,  on  the  opposite 
side  of  the  gulch,  and  on  Breece  hill  (6)  the  Highland  Chief  group,  overlooking  Evans  gulch.  On  Yankee  hill  are 
the  Andy  Johnson,  Chieftain,  Scooper,  and  others.  While  in  Stray  Horse  gulch  the  Double  Decker  and  adjoining 
mines  have  gold  ore  in  the  low"er  quartzite,  the  Adelaide  and -Argentine  find  carbonates  of  lead  at  the  contact  of 
the  White  pdrphyry  and  fhe  upper  portion  of  the  Silurian  formation. 

MINERALS. — The  most  common  minerals  are  cerussite,  anglesite,  pyromorphite,  and  galena ;  chloride,  chloro- 
bromide  and  rarely  iodide  of  silver;  iron,  generally  as  hydrated  sesquioxide,  but  in  the  Breece  iron  mine  as  red 
hematite  and  magnetite,  also  in  the  deeper  workings  in  the  form  of  pyrite;  manganese  generally  as  a  sort  of 
wad,  and  frequently  also  as  pyrolusite;  zinc  as  calamine  or  silicate,  and  in  depth  as  zincblende;  bismuth  as 
sulphide  and  as  sulpho-carbonate  in  the  Florence  mine;  vanadium  as  dechenite,  or  vanadate  of  lead  and  zinc,  in 
the  Morning  Star  and  Evening  Star  mines.  More  rarely,  native  sulphur  is  found  as  a  decomposition  product  of 
galena ;  also  native  gold  and  silver  in  the  limestone  deposits.  Arsenic  and  antimony  show  themselves  in  the 
products  of  the  smelters,  the  former  very  persistently,  but  are  seldom  found  as  definite  minerals  in  the  ores. 

Outside  the  California  district,  the  principal  mine  is  the  Homestake,  on  Homestake  peak,  in  the  northwestern 
corner  of  the  county,  which  was  developed  before  the  discovery  of  the  silver  ores  of  Leadville.  It  is  a  rich  body 
of  argentiferous  galena  in  Archaean  gneiss,  and  is  said  to  have  produced  at  one  time  a  considerable  quantity  of 
nickel  ore  in  the  form  of  an  arsenical  nickel  mineral  supposed  to  be  gersdormte.  A  number  of  less  important  mines 
have  been  developed  along  the  western  slopes  of  the  Sawatch  range  in  the  Archa3an  which  have  produced  small 
quantities  of  pyritiferous  ores  carrying  galena.  Their  main  value  lies  in  the  silver  which  they  contain,  which  is  also 
accompanied  by  a  certain  amount  of  gold.  They  are  mostly  reduced  in  the  amalgamating  mills  which  have  been  erected 
at  Leadville  for  treating  the  few  siliceous  ores  of  the  district  which  are  free  from  lead.  The  comparative  poverty 
of  the  mineral  deposits  of  this  district  in  gold  is  remarkable  when  one  considers  the  exceptional  richness  of 
many  of  its  placers.  In  the  normal  silver  deposits  of  Leadville  gold  is  present,  if  at  all,  in  very  minute  quantities; 
so  that  it  is  not  detected  by  the  assayer,  but  is  only  found  concentrated  in  the  bullion.  That  it  exists,  however,  is 
proved  by  its  having  been  found  occasionally  in  the  state  of  native  gold  in  the  limestone  deposits  ;  for  instance,  in 
those  of  the  Florence  mine. 

GUNNISON  COUNTY. 

Guunison  county  lies  to  the  west  of  Lake  and  Chaffee  counties,  its  eastern  boundary  being  formed  by  the  crest 
of  the  Sawatch  range.  It  originally  included  only  the  mountainous  country  connected  with  this  range  and  the 
group  of  the  Elk  mountains  which  branch  off  from  it  in  a  northwesterly  direction.  Since  the  recent  cession  of  the 
lands  of  the  Ute  Indian  reservation  it  also  includes  a  large  portion  of  this  reservation  in  the  Colorado  plateau 
region,  extending  to  the  boundary  of  Utah.  Its  present  area  of  11,338  square  miles  is  greater  than  that  of  any 
county  in  the  state. 

The  plateau  region,  as  yet  comparatively  unexplored,  is  mainly  occupied  by  nearly  horizontal  beds  of  Cretaceous 
and  Tertiary  age.  Except,  therefore,  where  the  underlying  Archaean  rocks  have  been  exposed  by  deep  erosion,  or 
the  later  formations  have  been  traversed  by  masses  of  eruptive  rock,  this  region  affords  little  promise  of  return 
to  the  prospector  in  his  search  after  deposits  of  the  precious  metals.  In  the  eastern  mountainous  region,  on  the 
other  hand,  the  geological  conditions  are  such  as  to  lead  one  to  expect  widespread  and  important  deposits  of 
metallic  minerals.  Owing  to  its  isolated  condition,  being  separated  from  the  rest  of  Colorado  by  high  mountain 
ranges  whose  lowest  passes  are  over  10,000  feet  high,  and  having  been  but  recently  reached  by  lines  of  railroad,  but 


78  PRECIOUS  METALS. 

few  actually  producing  mines  have  yet  been  developed  within  its  limits.  In  spite  of  the  fact  that  it  is  penetrated  by 
two  lines  of  railroad,  the  Denver  and  Eio  Grande  and  the  Denver  and  South  Park,  its  conditions  would  be  unfavorable 
for  the  treatment  of  low-grade  ores — the  true  source  of  wealth  of  a  mining  region — on  account  of  the  high  grades  -which 
have  to  be  overcome  by  these  roads  in  reaching  it,  and  which,  therefore,  enhance  the  cost  not  only  of  supplies,  but  of 
the  movement  of  ore  and  fuel,  were  it  not  for  the  fact  that  it  contains  within  itself  the  means  for  treating  its  own 
ores  at  low  cost  in  its  coal  beds,  which  are  not  only  exceptionally  well  situated  for  mining,  but  are  of  a  quality 
probably  superior  to  any  on  the  eastern  slope  of  the  mountains.  On  the  completion  of  the  extension  of  the  former 
road  to  Utah  it  will  have  an  additional  outlet  in  that  direction,  free  from  the  drawback  of  exceptionally  heavy 
grades. 

The  geology  of  the  western  slope  of  the  Eocky  mountains  presents  certain  contrasts  to  that  of  the  eastern.  In 
the  latter  region,  although  along  certain  shore-lines,  by  unequal  erosion,  beds  of  different  horizons  are  found  abutting 
against  the  underlying  Archajan,  in  general  the  lowest  Cambrian  beds  are  those  which  rest  directly  upon  it.  In 
the  western  region,  on  the  other  hand,  erosion  discloses  crystalline  gneisses  and  granites,  presumably  belonging 
to  the  Archaean,  in  direct  contact  with  horizons  as  high  as  the  Cretaceous,  and  at  points  far  removed  from  any 
well-defined  shore-line.  The  sedimentary  beds  also  dift'er  somewhat  in  lithological  constitution,  and  are,  as  a,  rule, 
considerably  thicker  than  corresponding  beds  on  the  eastern  slope.  Again,  the  coal-forming  period,  which  on  the 
eastern  slope  was  at  the  very  close  of  the  Cretaceous  (or,  as  some  have  maintained,  at  the  commencement  of  the 
Tertiary),  in  the  western  region,  .to  judge  from  the  testimony  of  the  thickness  of  beds  overlying  it,  occurred 
considerably  before  the  close  of  this  epoch.  The  ore  deposits  also,  which  there  are  found  mainly  in  the  Archaean  or 
Palaeozoic  formations,  in  the  Gunnisou  region  are  found  to  occur  also  in  the  Mesozoic  formations  even  as  late  as  the 
uppermost  portion  of  the  Cretaceous.  The  bituminous  coals  of  the  Cretaceous  formation,  which  are  generally  called 
lignites,  but  not  it  seems  with  absolute  propriety,  are  here  locally  transformed  into  semi -bituminous  and  even  into 
anthracite  coals  of  excellent  quality. 

The  geological  structure  of  the  Elk  Mountain  region  is  one  of  such  extreme  complexity  that  only  the  barest 
and  most  general  outlines  can  be  presented  in  the  limited  space  here  allotted.  According  to  Mr.  W.  H.  Holmes,  its 
structure  is  that  of  a  great  fault-fold,  ?.  e.,  an  anticlinal  fold,  running  generally  with  the  axes  of  the  range  and 
broken  along  its  crest  by  a  fault,  the  eastern  slope  of  the  anticlinal  being  relatively  gentle,  but  the  western  so 
steep  that  in  one  portion  the  beds  are  actually  inverted.  Of  the  sedimentary  beds  involved  in  this  fold  only  the 
Carboniferous,  Trias,  and  Jura  have  escaped  erosion  in  the  higher  portion  of  the  mountains,  while  the  Cretaceous 
beds  are  left  along  its  flanks.  In  the  center  of  this  fold  Mr.  Holmes  places  a  mass  of  eruptive  granite.  The  writer 
has  had  no  opportunity  of  verifying  Mr.  Holmes'  observations  in  the  center  of  the  range,  but  is  quite  ready  to  accept 
his  solution  of  the  structural  problems  involved,  while  making  a  mental  reservation  as  to  the  existence  of  eruptive 
granite  at  this  point.  From  observations  made  during  a  hasty  visit  to  the  southern  slopes  of  the  range  along  Slate 
creek  and  the  heads  of  Ohio  and  Anthracite  creeks  he  is  inclined  to  think  that  this  eruptive  body  may  belong,  as 
do  the  eruptive  masses  there,  to  the  porphyries  of  Mesozoic  age  and  of  the  Mount  Lincoln  type,  already  described 
in  the  section  on  Park  county.  These  rocks  here  break  through  the  Cretaceous  strata,  not  only  in  narrow  and 
well-defined  dikes,  but  in  immense  masses,  forming  entire  mountains  of  most  picturesque  outline,  of  which  Crested 
butte  and  Gothic  peak  form  the  simplest  type,  relics  of  nearly  horizontal  Cretaceous  strata  extending  up  their 
sides  for  several  hundred  feet  above  the  bottoms  of  the  present  valleys.  These  porphyries  in  .the  region  visited 
are  indicated  on  the  Hayden  map  either  as  eruptive  granites  or  as  Tertiary  volcanic  rocks.  Since  they  break  through 
the  Cretaceous  beds,  they  must  have  been  erupted  in  post-Cretaceous  times,  but  probably  before  the  deposition  of 
any  distinctly  Tertiary  beds,  and  their  mode  of  occurrence  and  lithological  characteristics  are  quite  different  from 
those  of  Tertiary  volcanic  rocks.  The  intrusion  of  such  enormous  masses  of  molten  material  has  produced  an 
extensive  and  widespread  metamorphism  of  the  sedimentary  beds,  and  may  probably  account  for  the  change  of  the 
bituminous  coals  to  anthracite. 

The  Elk  mountains  are  evidently  of  later  age  than  the  Sawatch,  and,  very  possibly,  even  later  than  the  Mosquito 
or  Park  range.  The  ore  deposits  of  the  Ruby  district  must  be  of  post-Cretaceous  age,  since  they  traverse  Cretaceous 
rocks ;  but  as  to  the  age  of  deposits  occurring  in  the  older  rocks  no  data  are  yet  at  hand.  Ore  has  been  found 
in  almost  every  portion  of  the  Elk  mountains  and  on  the  flanks  of  the  Sawatch.  The  principal  mining  centers  are 
Aspen,  on  the  northeast  slope  of  the  Elk  mountains,  and  Independence,  on  the  west  slope  of  the  Sawatch,  in  the 
drainage  of  Eoaring  Fork;  Euby,  Gothic,  and  a  number  of  small  towns  on  the  southwest  slope  of  the  Elk  mountains  ; 
and  Pitkin  and  Tin  Cup,  on  the  southwest  slope  of  the  Sawatch.  At  Independence  sulphuret  ores  carrying  silver  are 
found  in  the  Archaean.  The  Gold  Cup  mine,  near  Alpine  pass,  in  the  Tin  Cup  district,  occurs  in  a  black,  fine-grained 
limestone,  not  unlike  the  Carboniferous  limestones  of  the  Mosquito  range.  Its  ore  is  a  silver-bearing  cerussite, 
associated  with  some  oxide  of  copper  in  a  ferruginous  and  siliceous  gangue.  Of  the  ore  deposits  occurring  in  the 
Cretaceous  rocks  in  Euby  district  the  Forest  Queen  mine  may  be  taken  as  a  type.  The  vein  material  seems  to  be 
a  decomposed  porphyry;  probably  a  narrow  dike  traversing  the  Cretaceous  sandstones,  and  standing  in  an 
approximately  vertical  condition.  The  ore  is  largely  ruby  silver  and  arsenical  pyrite,  occurring  in  small  crevices  and 
fissures  in  the  decomposed  porphyry.  The  gangue  material  is  sometimes  simply  an  indistinctly  banded  quartz. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  79 

CHAFFEE  COUNTY. 

Chaft'ee  county  occupies  the  valley  of  the  Arkansas  river  between  the  crests  of  its  bounding  ranges  from  the 
southern  boundary  of  Lake  county  down  to  Fremont  and  Saguache  counties,  a  little  below  the  mouth  of  the  South 
Arkansas.  Its  mountain  slopes  are  composed  of  Archaean  rocks,  mainly  granite,  traversed  by  porphyry  dikes, 
with  occasional  remnants  of  Palaeozoic  formations  in  the  southern  parts  which  have  escaped  erosion  resting 
on  their  crests.  The  valley  bottom,  as  in  Lake  county,  contains  stratified  beds  of  gravelly  formation  and  of  recent 
date ;  but  whether  they  are  of  the  same  age  as  the  Lake  beds  of  Lake  county,  or  have  been  formed  in  the  Tertiary 
period,  is  not  yet  definitely  known.  The  more  recent  gravel  deposits  at  the  mouth  of  the  larger  canons,  as  well 
as  those  along  the  bed  of  the  Arkansas  river,  yield  gold.  The  richest  are  those  at  Cash  creek,  which  have  been 
worked  since  the  earliest  discovery  of  minerals  in  this  portion  of  the  country. 

Its  mining  districts  have  but  few  developed  mines,  hence  data  with  regard  to  them  are  extremely  meager. 
In  the  neighborhood  of  the  town  of  Granite  gold-bearing  veins  have  been  worked  on  the  east  side  of  the  valley  in 
former  years.  Near  Buena  Vista,  also  on  the  east  side,  is  the  Free  Gold  district,  so  called  from  the  Free  Gold  mine, 
which  is  an  auriferous  quartz  vein  in  a  syenite  containing  abundant  titanite.  The  foot-wall  specimen  differs  from 
that  of  the  hanging  wall,  which  suggests  the  possibility  that  the  vein  may  be  on  a  fault-plane. 

The  Chalk  Creek  district  toward  Alpine  pass,  on  the  opposite  side  of  the  valley,  shows'  also  syenttic  country 
rock  which  contains  a  little  quartz.  The  mines  from  which  specimens  were  obtained  are  the  Black  Hawk.  Mary 
Murphy,  and  Hortense.  The  vein  material  of  the  two  former  is  a  felsitic  mass  which  may  be  a  decomposed  porphyry. 
In  the  ore  specimen  the  only  recognized  minerals  are  pyrite  and  a  black  mineral  which  seems  to  contain  manganese. 
The  ore  of  the  Horteuse  is  a  decomposed  quartz-porphyry,  from  which  some  metallic  mineral  has  been  removed  by 
solution. 

The  Monarch  district  is  near  the  head  of  one  of  the  branches  of  the  South  Arkansas  river.  The  Monarch  mine, 
from  which  its  name  is  derived,  is  a  limestone  deposit,  occurring  between  a  dark-gray  limestone  above  and  a  fine- 
grained white  limestone  below.  The  horizon  of  these  limestones  is  not  known,  but  it  is  very  possible  that  they 
correspond  to  the  Bine  and  White  limestones  of  Leadville.  The  ore,  like  that  of  Leadville,  is  mainly  cernssite  or 
carbonate  of  lead.  The  Columbus  mine,  in  the  same  district,  occurs  in  granite,  its  ore  consisting  of  fragments  and 
crystals  of  quartz,  cemented  together  by  some  metallic  mineral  colored  red  or  yellow  by  oxide  of  iron. 

DOUGLAS  COUNTY. 

Douglas  county  lies  south  of  Arapahoe  county,  and  extends  as  far  as  the  divide  between  the  Platte  and  Arkansas 
rivers  and  east  of  Jefferson  county,  including  a  portion  of  the  Colorado  range  lying  east  of  the  Platte  canon.  As 
is  the  case  further  north,  this  portion  of  the  range  is  not  yet  found  to  contain  valuable  metallic  minerals.  The 
coal  rocks,  however,  underlie  the  plain  country  east  of  the  foot-hills,  though  as  one  approaches  the  divide  they  are 
more  and  more  deeply  buried  beneath  the  Tertiary  deposits  of  which  this  mesa-like  ridge  is  formed.  Their  outcrops 
can  be  traced  from  the  Platte  canon  to  the  southern  borders  of  the  county,  approaching  nearer  and  nearer  to  the 
foot-hills  as  one  proceeds  southward. 

In  the  neighborhood  of  Castle  Eock  are  mesa-like  ridges,  which  extend  almost  continuously  to  the  eastward; 
but  west  of  the  railroad,  and  between  it  and  the  foot-hills,  these  ridges  are  broken  by  erosion  into  a  series  of  isolated 
buttes,  and  are  made  up  of  gravel  and  coarse  conglomerate  derived  from  the  Archaean  formation,  belonging  to  the 
Monument  Creek  Tertiary  of  the  Haydeii  survey,  whose  age  has  not  yet  been  determined.  In  the  neighborhood  of 
Castle  Kock,  and  for  some  six  or  eight  miles  to  the  southward,  the  surfaces  of  these  mesas  are  covered  by  a  light 
pinkish-colored  rhyolitic  tufa,  which  forms  au  admirable  building-stone,  and  has  been  very  extensively  used  for 
this  purpose  in  Denver.  The  outlines  of  this  volcanic  flow  have  not  yet  been  accurately  determined ;  it  extends 
but  a  short  distance  east  and  west,  and  has  an  average  thickness  of  about  20  feet. 

EL  PASO  COUNTY. 

More  than  half  of  the  area  of  El  Paso  county,  which  lies  to  the  south  of  Douglas,  is  plain  country.  Its  western 
mountainous  area  includes  the  partially  isolated  mass  of  Pike's  peak,  separated  from  the  main  Front  range  by  Dte 
pass  and  Manitou  park,  which  once  constituted  a  bay  or  arm  of  the  Palaeozoic  sea. 

The  only  mineral  of  industrial  importance  thus  far  developed  is  coal,  of  which  working  mines  exist  to  the  east 
of  Colorado  Springs.  Prospectors  after  the  precious  metals  on  Pike's  peak  have,  however,  developed  au  extremely 
interesting  series  of  minerals,  of  which  those  of  the  cryolite  group  may  possibly  prove  of  economic  importance. 
The  following  are  the  species  previously  recognized : 

Microcline,  as  green  amazou  stone  and  other  colors;  albite;  biotite,  var.  siderophyllite ;  quartz,  clear  and 
smoky;  fluorite;  coluuibite;  gothite:  hematite  and  limouite  as  pseudornorphs  after  siderite:  artvedsonitf; 
astrophyllite ;  zircon. 

In  addition  to  the  above  the  following  have  recently  been  determined  by  the  members  of  the  Kocky  Mountain 
division  of  the  United  States  geological  survey: 

Topaz,  phenacite,  kaoliuite,  a  peculiar  greeir  muscovite,  cryolite,  thomsenolite,  gearksutite,  and  other  fluorides 
not  yet  definitely  determined.  • 


80  PRECIOUS  METALS. 

FREMONT  COUNTY. 

Fremont  county,  which  lies  to  the  east  of  Chafl'ee  and  Saguache  counties,  includes  the  canon  valleys  of  the 
Arkansas  after  it  bends  to  the  eastward  arid  a  portion  of  the  plain  country  beyond  Canon  City.  Its  mountains 
have  a  base  of  Archaean,  which  in  the  western  portion  of  the  county  is  covered  by  Palaeozoic  formations,  and  on  the 
north,  toward  the  South  park,  by  Tertiary  eruptive  rocks,  with  probably  some  older  porphyries.  Along  the  foot-hills 
at  Canon  City  occur  the  upturned  Triassic  and  Cretaceous  rocks,  which  furnish  valuable  building- stones.  A 
limestone  of  the  Colorado  Cretaceous,  which  is  remarkably  pure,  is  used  in  making  lime  and  as  a  flux  for  smelting- 
works.  From  less  pure  limestone  above  the  Triassic  hydraulic  cement  is  made.  From  'Jurassic  and  Lower 
Cretaceous  beds  in  the  plains,  as  well  as  in  the  valley  of  Oil  creek,  petroleum  has  been  obtained,  and  several  wells, 
some  over  1,000  feet  in  depth,  have  been  sunk.  As  yet  no  considerable  concentrations  of  oil  have  been  developed. 
South  of  Cafion  City  is  a  synclinal  basin  in  which  the  Laramie  beds  have  escaped  erosion,  and  where  valuable  coal 
mines  have  been  opened  by  the  railroad  companies. 

CUSTER  COUNTY. 

Custer  county  lies  to  the  south  of  Fremont,  and  comprises  the  Wet  Mountain  valley,  lying  between  the  Wet 
mountains  or  Greenhorn  range  on  the  east  and  the  north  end  of  the  Sangre  de  Cristo  range  on  the  west.  The 
former  mountains  are  a  southern  continuation  en  echelon  of  the  Front  or  Colorado  range,  and  consist  of  Archaean 
rocks,  mainly  granite,  with  Mesozoic  formations  resting  against  its  eastern  base.  This  range  is  relatively  low,  and 
its  slopes  gentle,  except  where  cut  through  by  deep  canons.  The  Sangre  de  Cristo  range,  on  the  other  hand,  which 
is  a  southern  continuation,  also  en  echelon,  of  the  Mosquito  or  Park  range,  is  a  lofty  imposing  chain,  whose  rugged 
outlines  suggest  a  very  diifereut  composition.  It  has  not  been  examined  by  the  writer,  but  presumably  consists  of 
the  same  Palaeozoic  rocks  that  are  found  in  the  Mosquito  range,  resting  on  an  Archaean  base  and  traversed  by 
Secondary  eruptive  ro«ks,  of  which  the  so-called  Sangre  de  Cristo  granite,  outlined  on  the  Hayden  map,  is  very 
possibly  a  variety.  The  Wet  Mountain  valley  at  its  widest  point  comprises  a  distance  of  over  20  miles  from  east  to , 
west  between  the  crests  of  these  bounding  ridges.  The  valley  bottom  lies  near  the  west  side  of  this  depression,  its 
Quaternary  covering  resting  either  on  the  Archaean,  or  on  the  eruptive  rocks  which  have  broken  through  it. 

The  principal  mines  have  been  developed  in  the  neighborhood  of  the  towns  of  Silver  Cliff  and  Bosita,  and  an 
area  of  10  miles  east  and  west  and  6  miles  north  and  south  includes  the  greater  portion  of  these.  In  this  area  the 
underlying  Archaean  is  broken  through  and  covered  by  Secondary  eruptive  rocks,  among  which  diabase  is  the  only 
type  which  has  as  yet  been  definitely  determined.  To  these  eruptions  have  succeeded  flows  of  andesite  and 
rhyolite,  which  outcrop  at  Bosita  and  Silver  Cliff. 

The  town  of  Rositu  is  situated  near  the  eastern  end  of  the  district,  in  the  midst  of  a  group  of  steep  hills  with 
smooth  rounded  slopes,  which  project  out  into  the  valley  from  the  Wet  Mountain  range.  The  town  of  Silver  Cliff, 
about  six  miles  west  of  Eosita,  is  situated  on  the  open  plain  near  a  mesa-like  ridge,  on  whose  cliff  face,  from 
which  the  town  derives  its  name,  are  found  the  silver  deposits  of  the  Eacine  Boy  mine.  The  rock  of  which  this 
cliff  is  formed  is  a  light  pinkish-colored  rhyolite,  showing  the  characteristic  finely  laminated  or  fluidal  structure. 
In  the  town  itself,  and  along  the  eastern  edge  of  the  cliff,  are  outcrops  of  a  dark  pitchstone,  probably  a  hyaline 
variety  of  the  rhyolite.  Outcrops  of  granite  are  found  on  the  plains  between  Silver  Cliff  and  in  the  hills  around 
Eosita,  rendering  it  probable  that  the  rhyolite  rests  directly  on  the  underlying  Archa3an.  A  number  of  isolated 
hills  rise  out  of  these  plains,  the  most  prominent  of  which  is  Bound  mountain,  on  which  is  situated  the  Plata 
Verde  mine,  and  about  two  miles  to  the  northward  are  the  Blue  mountains,  in  which  is  situated  the  Bull-Domingo 
mine.  The  bottom  of  the  valley,  through  which  runs  Grape  creek,  lies  still  to  the  west  of  Silver  Cliff,  and  has  a 
considerable  extent  of  arable  land. 

ORE  DEPOSITS. — The  ore  deposits  of  this  region  are  in  many  cases  rather  exceptional  in  character,  and  have 
given  rise  to  considerable  speculation  as  to  their  origin.  As  yet,  however,  no  systematic  or  exhaustive  study  has 
been  made  of  them  on  which  to  found  a  definite  and  satisfactory  classification.  Most  prominent  and  remarkable  are 
the  Bassick  and  the  Bull-Domingo,  each  situated  near  the  northern  limits  of  the  eruptive  rocks,  the  former  a  short 
distance  north  of  Eosita,  the  latter  7  miles  westward,  correspondingly  situated  with  regard  to  Silver  Cliff.  The 
characteristic  feature  common  to  these  two  mines  is  that  the  ore  is  found  in  large  bodjes  without  any  definite 
boundary,  forming  a  coating  on  irregularly-rounded  fragments  of  the  country  rock.  A  favorite  method  of  accounting 
for  this  mode  of  occurrence  has  been  that  the  ore  cavities  are  old  craters  or  solfataric  openings,  in  which  the 
fragments  of  country  rock  have  been  tossed  about  and  rounded  by  attrition  and  coated  by  a  deposition  from  metallic 
A-apors  and  solutions.  While  the  known  facts  with  regard  to  these  deposits  are  insufficient  to  afford  a  positive 
theory  with  regard  to  their  origin,  the  evidence  is  decidedly  against  this  somewhat  startling  hypothesis.  The 
country  rock  of  the  Bull-Domingo  mine  is  a  hornblendic  gneiss,  and  therefore  probably  belongs  to  the 
Archaean.  The  ore,  which  is  mainly  an  argentiferous  galena,  forms  a  regular  semi-crystalline  coating  from  one- 
eighth  to  one-quarter  of  an  inch  in  thickness  around  the  bowlders  and  pebbles  of  country  rock,  and  fills  the  irregular 
interstices  between  them.  These  pebbles  are  not  in  direct  contact  one  with  the  other,  but  are  separated  by  the 
metallic  coating  belonging  to  each  individual  pebble.  The  galena)  is  frequently  covered  by  a  second  botryoidal 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  81 

coating,  probably  of  a  siliceous  nature.  The  deposit  is  from  40  to  60  feet  wide,  and  strikes  in  a  northwesterly 
direction.  No  fresh  specimens  of  the  country  rock  of  the  Bassick  mine  were  obtained,  and  its  exact  nature  is  not 
therefore  known.  It  is  said  to  be  the  same  on  both  sides  of  the  deposit,  and  to  be  an  eruptive  rock.  In  this  case  it 
is  probable  that  it  is  a  breccia,  and  the  ore  is  a  replacement  of  the  matrix.  According  to  Mr.  L.  R.  Grabill,  («)  the 
deposit  is  an  irregular  opening,  nearly  eFliptical,  in  horizontal  sections  from  20  to  100  feet  in  width,  and  standing 
generally  vertical  to  the  depth  of  present  developments,  i.  e.,  about  800  feet.  The  fragments  of  country  rock 
which  fill  this  opening  vary  in  size  from  one  and  a  half  feet  in  diameter  to  the  smallest  dimensions.  They  are  rarely, 
if  ever,  in  actual  contact  with  each  other,  while  the  metallic  shells  which  surround  them  are  tangent.  The  size  of 
the  fragments,  as  well  as  the  quantity  of  ore  or  metallic  mineral  present,  decreases  from  the  center  outward,  without 
any  definite  limit  having  yet  been  determined.  In  the  shell  or  metallic  coating  which  surrounds  these  fragments 
Mr.  Grabill  distinguishes  a  series  of  concentric  layers,  the  innermost  and  thinnest  consisting  of  a  mixture  of  sulphides 
of  lead,  antimony,  and  zinc,  carrying  about  60  ounces  of  silver  and  from  1  ounce  to  3  ounces  of  gold  to  the  ton. 
This  layer  is  always  present.  A  second  coating,  not  always  found,  is  lighter  in  color,  and  contains  more  lead,  silver, 
and  gold.  The  third  shell  is  mainly  sphalerite  or  zincbleude,  reaching  a  maximum  thickness  of  5  centimeters, 
which  carries  from  60  to  100  ounces  of  silver,  and  from  15  to  50  ounces  of  gold  to  the  ton,  with  considerable  iron,  and 
some  copper.  This  constitutes  the  principal  pay-ore  of  the  mine.  The  fourth  coating,  when  present,  is  formed 
of  chalcopyrite,  but  is  much  more  irregular  than  the  previous  ones,  and  carries  as  high  as  from  50  to  100  ounces 
of  gold  and  silver.  Outside  of  these  a  fifth  thin  coating  of  pyrite  crystals  is  occasionally  found.  All  the  layers 
have  a  more  or  less  crystalline  structure.  The  remaining  interstices  between  the  pebbles  are  filled  with  kaolin. 
Another  singular  fact  connected  with  the  deposit  is  the  occurrence  of  small  fragments  of  charcoal  in  cavities  between 
the  bowlders  toward  the  outer  edges  of  the  ore  body,  and  most  commonly  near  the  water-level.  These  are  sometimes 
partially  mineralized,  and  at  others  are  perfectly  unaltered  and  retain  the  woody  structure.  The  greatest  depth  at 
which  they  have  been  found  is  765  feet  from,  the  surface.  The  other  minerals  found  in  the  mine  are  calamine, 
smithsonite,  jamesonite,  tetrahedrite,  free  gold,  and  tellurides  of  silver  and  gold  in  minute  quantities. 

Another  type  of  deposit  in  the  region  fills  more  or  less  vertical  fissures  traversing  the  eruptive  rocks  which  form 
the  hill  country  around  Kosita.  The  principal  of  these  is  the  Humboldt-Pocahontas  vein,  running  northwest  and 
southeast,  a  short  distance  north  of  the  town.  The  exact  character  of  the  country  rock  is  not  definitely  known. 
This  ore  carries  chalcopyrite  and  fahlerz,  with  a  little  siderite,  in  a  gangue  of  barite. 

The  Eacine  Boy  mine,  near  Silver  Cliff,  forms  a  third  distinctive  type,  and  seems  to  be  an  irregular  impregnation 
of  the  country  rock,  the  ore  in  general  showing  a  little  black  staining  of  some  manganese  mineral  as  its  only  visible 
metallic  constituent.  Thin  films  of  chloride  of  silver  are  sometimes  distinguishable.  This  is  a  free-milling  ore  ef 
comparatively  low  grade,  but  valuable  on  account  of  its  great  mass.  Plata  Verde  mine  has  not  been  worked  since 
its  mill  was  finished,  and  no  data  are  available  in  regard  to  the  character  of  its  deposit,  which  is,  however,  in  rhyolitic 
rock.  The  ore  is  chloride  of  silver,  with  some  snlphurets,  impregnating  the  country  rock.  The  Terrible  mine,  in  the 
Archrcan,  is  about  12  miles  northeast  of  Silver  Cliff,  and  has  a  foot  wall  of  fine-graiued  iron-stained  gneiss.  The 
vein  strikes  N.  20°  W.,  and  dips  78°  NE.  Its  ore  consists  of  a  massive  cerussite,  sometimes  cementing  fragments 
of  wall  rock,  the  gangue  material  being  decomposed  country  rock.  The  Gem,  a  newly-opened  mine  some  12  miles 
north  of  this  district,  is  interesting  as  having  afforded  specimens  of  a  rich  nickel  ore.  On  Grape  creek,  in  the 
northern  portion  of  the  county,  a  considerable  body  of  titaniferous  magnetite  has  also  been  discovered.  Both  these 
last-named  deposits  are  probably  in  the  Archsean. 

Ore  deposits  have  also  been  developed  on  the  east  slope  of  the  Sangre  de  Cristo  range  about  7  miles  west  of 
Silver  Cliff.  The  Verde  mine  has  a  vein  striking  N.  50°  W.,  and  dipping  60°  SW.,  said  to  be  in  granite.  Its  ore  is 
a  mixture  of  pyrite  and  chalcopyrite,  with  fahlerz. 

HUEEFANO  COUNTY. 

Huerfauo  county,  lying  south  of  Custer  and  Pueblo,  is  largely  a  plain  country,  and  only  its  eastern  end,  which 
includes  Huerfano  park,  a  southern  continuation  of  the  Wet  Mountain  valley,  extends  into  the  mountain  region. 
The  surface  of  the  plain  country,  as  well  as  the  bottom  lands  of  Huerfano  park,  which  was  a  bay  in  the  original 
Archrean  shore-line,  is  covered  by  Cretaceous  deposits ;  and  it  is  only  along  the  crests  of  the  bounding  ridges,  the 
Wet  mountain  and  the  Sangre  de  Cristo,  and  near  the  eruptive  mass  of  the  Spanish  peaks,  that  the  rocks  liable  to 
carry  metallic  minerals  are  exposed. 

The  schedule  reports  furnish  data  from  only  a  single  mine,  the  Mountain  Monarch,  in  the  Third  Judicial 
district.  This  mine  is  situated  on  the  north  slope  of  the  West  Spanish  peaks,  about  10  miles  south  of  La  Veta.  Its 
deposit  is  said  to  be  a  fissure  vein  running  east  and  west,  with  a  shallow  dip  south,  and  is  from  3  to  6  feet  wide. 
The  ore  is  a  banded  vein  material,  consisting  of  galena,  pyrite,  chalcopyrite,  and  fahlerz.  The  country  rock  is  said 
to  be  granite,  and  the  gangue  material  porphyry.  No  specimens  of  either  were  sent  in,  but  it  seems  probable  to  the 
writer  that  both  belong  to  the  crystalline  quartz  porphyries,  whose  mode  of  occurrence  has  been  already  described, 
and  which  correspond  with  what  is  known  of  the  eruptive  mass  of  the  Spanish  peaks. 

a  Trans.  A.  I.  M.  E.,  August,  1882. 
VOL  13 6 


82  PRECIOUS  METALS. 

THE  SAN  JUAN  REGION. 

GEOLOGY. — The  San  Juan  mining  region,  which  embraces  San  Juan  county,  with  the  adjoining  counties  of 
Hinsdale,  Ouray,  La  Plata,  and  portions  of  Rio  Grande  and  Concjos  counties,  takes  its  name  from  the  San  Juan 
mountains,  a  lofty  and  irregular  mass,  which,  like  the  Elk  mountains,  have  a  general  northwest  trend,  but  are  of 
still  more  irregular  structure,  and  have  an  even  greater  predominance  of  eruptive  rocks.  Owing  to  the  prevalence 
of  the  latter,  which  constitute  the  mass  of  a  great  portion  of  the  mountain  region,  the  structure  of  the  sedimentary 
beds  is  necessarily  very  indistinct,  and  the  geological  data  which  are  obtainable  are  of  the  most  unsatisfactory 
nature.  The  eruptive  rocks  occur  in  great  masses,  sections  2,000  and  ;5,0()0  feet  thick  being  shown  in  the  different 
canons,  their  most  characteristic  and  striking  feature  being  the  occurrence  of  immense  breccia  beds  over  wide 
areas  throughout  the  region.  The  entire  mass  of  these  rocks  has  been  classed  by  the  members  of  the  Haydeu 
survey  among  the  Tertiary  eruptives,  and  they  have  been  colored  on  the  map  as  either  trachytes  or  basalts. 
While  basalts  undoubtedly  do  occur,  and  trachytes  may  be  found,  these  or  later  flows  cover  bodies  of  earlier 
eruptive  rocks,  and  it  seems  probable  to  the  writer  that  tdie  deposits  in  the  region  will  be  found  to  occur  mainly 
in  the  latter.  This  idea  is  supported  by  the  examination  of  the  specimens  of  the  country  rock  brought  in  by  census 
experts.  Although  these  specimens  were  mainly  in  a  condition  of  alteration  so  far  advanced — as  is  common  among 
eruptive  rocks  in  the  neighborhood  of  mines — that  their  original  condition  could  rarely  be  definitely  determined, 
some  undoubted  porphyries,  diorites,  and  diabases  occur  among  them,  and  the  others  can  be  referred,  with  more 
or  less  probability,  to  varieties  of  one  of  these  types,  while  among  the  eighteen  specimens  which  were  examined 
microscopically  only  a  single  undoubted  Tertiary  rock  (basalt)  was  found.  This  occurs  as  the  foot  wall  of  the  Ohio 
Consolidated  mine,  in  Hinsdale  county.  In  some  of  the  valleys  erosion  has  exposed  granite  and  gneiss,  presumably  of 
Archaean  age,  underlying  these  eruptives.  At  the  head  of  the  Uncompahgre  river,  near  Ouray,  beds  of  Paheozoic  and 
Lower  Mesozoic  age  are  found  resting  on  the  granite  and  sinking  to  the  northwest  under  the  Cretaceous  formations. 
The  latter  cover  the  western  portions  of  the  counties  of  Ouray  and  La  Plata,  which,  like  those  of  Gunnison  and 
Grand  counties,  belong  to  the  Colorado  plateau  region.  On  the  southern  slopes  of  the/  San  Juan  mountains,  in  San 
Juan  county  and  the  northeastern  corner  of  La  Plata  county,  there  is  exposed  a  considerable  area  of  Palaeozoic  rocks, 
which  to  the  southward  pass  under  the  Cretaceous  formations  of  the  valley  of  the  San  Juan.  A  large  portion  of 
these  are  of  undoubted  Carboniferous  age.  but  adjoining  the  valley  of  the  Animas,  on  the  east,  is  a  mountainous 
region  called  the  Quartzite  peaks,  composed  of  rocks  whose  age  is  a  matter  :of  considerable  uncertainty.  Th« 
limestones  which  adjoin  the  quartzite  have  been  considered  by  Dr.  Eudlich  as  Devonian  mainly  on  the  evidence  of  a 
single  well-defined  fossil.  This  fossil  is,  however,  pronounced  by  Professor  R.  P.  Whittteld  to  be  a  Carboniferous  and  not 
a  Devonian  type.  The  quartzite  formations,  which  are  supposed  to  underlie  these,  are  called  on  the  map  Metamorphic- 
Palseozoic,  the  rubric  of  this  formation,  however,  being  included  in  the  Archaean;  a  seeming  contradiction  of  terms 
of  which  the  writer  has  found  no  explanation.  It  is  probable  that  thePaheozoic  formations  thicken  to  the  southward, 
as  they  are  known  to  do  to  the  westward;  and  since  the  Devonian  is  well  developed  in  Utah  and  Nevada,  and  fossils 
of  the  Waverly  type  have  recently  been  found  in  Lake  valley,  New  Mexico,  it  is  very  possible  that  this  formation 
may  be  represented  in  the  region,  but  its  existence  cannot  yet  be  considered  as  determined. 

ORE  DEPOSITS. — The  most  striking  feature  in  the  mineral  development  of  the  San  Juan  region  is  the  immense 
quartz  veins  traversing  the  eruptive  rocks,  which  stand  nearly  vertical,  their  outcrops  projecting  like  walls  from  the 
surface,  and  often  traceable  to  a  depth  of  several  thousand  feet  along  the  sides  of  the  deep  valleys  and  canons. 
According  to  Mr.  R.  C.  Hills,  these  veins  cross  both  the  older  eruptive  rocks  and  what  he  considers  as  the  overlying 
Tertiary  eruptives ;  but  it  is  only  in  rare  instances  that  the  latter  have  been  shown  to  inclose  valuable  ore  bodies,, 
these  being  found  generally  in  the  older  massive  or  brecciated  rocks,  whose  prevailing  color  is  some  shade  of  green. 
Veins  are  also  found  in  the  underlying  gneiss  and  granite ;  and  in  the  western  portion,  especially  in  the  neighborhood 
of  Rico,  are  deposits  in  limestones  of  Carboniferous  age,  frequently  along  bedding-planes  and  at  the  contact  with 
sheets  of  intrusive  igneous  rocks. 

The  deposits  of  the  region  are  mainly  argentiferous.  In  some,  however,  gold  is  the  chief  pay  mineral;  in 
others  both  gold  and  silver  occur.  Free-milling  gold  ores  are,  as  a  rule,  comparatively  rare,  the  majority  of  the 
ores  containing  a  large  admixture  of  base  metals,  so  that  they  require  smelting.  The  prevailing  minerals  are 
argentiferous  galena,  gray  copper,  generally  argentiferous  or  freibergite,  and,  in  the  upper  part  of  the  deposits^ 
native  silver  and  pyrargyrite  or  ruby  silver.  Bismuth-silver  minerals  are  found  in  several  mines  in  considerable 
quantities.  Gold  is  apparently  derived  in  most  part  from  pyrite.  Barite  is  not  uncommon  as  a  gaugne  material, 
and  fluorite  also  occurs,  although  more  rarely.  Compounds  of  antimony  and  tellurium  are  said  to  occur,  and  rarely 
molybdenite  and  some  nickel  minerals.  The  veins  are  said  to  have  a  banded  structure,  and  the  quartz  is  said  to 
be  crystalline.  It  must  be  noted,  however,  at  the  same  time,  that  in  many  cases  one  or  both  walls  are  not  well 
defined,  and  a  portion  at  least  of  the  vein  material  is  quite  frequently  decomposed  country  rock.  Of  the  age  of 
these  deposits,  in  the  uncertainty  which  exists  as  regards  the  true  character  of  the  various  country  rocks,  but  little 
can  be  definitely  said.  Mr.  Hills,  who  has  devoted  considerable  study  to  ore  deposits,  especially  those  of  Ouray 
county,  divides  the  veins  into  three  systems,  which  he  regards  as  distinct  and  probably  of  different  age:  First, 
silver-bearing  veins,  standing  at  high  angles  (80°  to  90°)  and  thin  (6  inches  to  3  feet  wide),  with,  no  gouge  or 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION. 


83 


selvage,  carrying  essentially  base-metal  ores.  Second,  gold-bearing  veins,  large  and  strong,  dip  about  60°,  gouge 
or  selvage  on  one  or  botli  walls,  intersecting  the  former,  and  tberefore  of  later  age.  His  tbird  class  differs  from  the 
first  only  in  being  wider  and  stronger  and  in  carrying  their  ore  in  persistent  bands  or  streaks.  Like  them,  they 
stand  at  u  high  angle,  and  sometimes  carry  bismuth  and  antimony  minerals.  These  veins  are  essentially  gold  bearing, 
as  even  when  carrying  base-metal  ores  they  contain  little  or  no  silver.  According  to  Mr.  T.  B.  Comstock,  in  an  article 
on  the  geology  of  San  Juan  county,  (a)  the  age  of  the  veins  of  the  district  is  probably  post- Tertiary,  and  in  their 
gradually  varying  strikes,  in  which  there  is  little  evidence  of  any  systematic  parallelism,  he  finds  a  tendency  to 
radiate  out  from  certain  points  which  he  considers  centers  of  trachytic  eruption.  As,  however,  in  the  nomenclature 
and  classification  of  eruptive  rocks,  he  follows  a  system  adopted  by  Dr.  Endlich,  and  which  is  peculiar  to  that 
gentleman,  the  writer  is  at  a  loss  to  know  what  value  to  place  on  his  evidence.  He  recognizes  a  primary  and 
secondary  system  of  veins,  the  latter  of  which  cross  the  former,  and  makes  the  following  provisory  classification: 
First,  those  having  a  northwest  trend,  which  are  pre-eminently  gray  copper  (freibergite)  lodes ;  second,  those  with 
an  east  and  west  trend,  the  bismuth  series  of  lodes,  carrying  occasionally  nickel  and  molybdenum  minerals;  third, 
those  with  a  northeast  trend,  the  telluride  series,  with  antimony  and  sulphides  of  the  precious  metals.  From  the 
data  gathered  by  census  experts,  which  are  necessarily  very  incomplete,  it  appears  that  hi  San  Juan  county  the 
northwest  trend  predominates;  in  the  Uncompahgre  district,  comprising  the  northern  portion  of  San  Juan  and  the 
adjoining  portion  of  Onray  county,  the  northeast  trend  predominates;  while  in  Ouray  county  these  two  directions 
are  about  equally  distributed,  the  east-and-west  trend  being  in  either  case  of  subordinate  importance. 

SAN  JUAN  COUNTY. 

Sail  Juan  county  has  an  area  of  only  560  square  miles,  and  includes  the  drainage  area  of  the  head  of  the  Aniinas 
river.  Its  mines  are  principally  found  in  the  lofty  peaks  which  surround  the  picturesque  and  elevated  basin  of 
Baker's  park  and  its  tributary  valleys.  They  occur  mainly  in  the  older  eruptive  rocks,  which  here  apparently  rest 
directly  on  a  base  of  gneiss  and  crystalline  schists,  presumably  of  Archaean  age. 

From  Baker's  park  southward  the  Animas  flows  in  deep  canons  cut  through  later  sedimentary  rocks,  which 
on  the  east  consist  mainly  of  the  questionable  series  classed  as  Mi'tamorphic- Palaeozoic,  and  on  the  west  of  limestones 
of  Carboniferous  age.  Of  the  later  eruptive  rocks  which  cover  those  of  Secondary  age  it  can  only  be  said  that,  in 
view  of  the  facts  developed  by  recent  more  exact  lithological  studies,  it  is  unfortunate  that  the  term  '•  trachyte" 
should  have  been  so  universally  applied,  inasmuch  as  late  investigations  of  other  districts  where  this  rock  was 
supposed  to  exist  in  large  masses  prove  the  normal  type  to  be  of  extremely  rare  occurrence. 

The  mines  reported  by  census  experts  belong  to  three  principal  districts:  the  Animas  district,  about  Baker's 
park  and  Silverton;  Eureka  district,  in  the  northeast  portion  of  the  county;  and  the  Uucompahgre  district,  on  the 
mountains  between  the  Uncompahgre  and  Animas  rivers,  which  apparently  takes  in  also  a  portion  of  Ouray  county. 
The  region  is  undoubtedly  one  of  exceptional  richness  in  mineral  developments,  so  that  Mr.  Comstock's  statement 
that  one-sixth  of  the  area  of  the  county  is  taken  up  by  lode  claims  seems  scarcely  an  exaggeration.  The  subjoined 
table  gives  a  brief  summary  of  the  data  obtained  from  producing  mines  by  census  experts: 


Mine. 


ANIXA8  IlIrtTKKT. 

A»pen  Groop 


Country  rock  and  vein. 


Ore  and  gangne. 


Bowery 

Cleveland  Consolidated.. 

Diamond  (Emblem  lode). 

Empire 

Hercule* 

Highland  Mary 


Jennie  Parker  . 
Molas... 


Greenish,  indistinct  porphyritlc  rock.     Undeterminable,     Vein 
strike,  NW.;  dip,  WPSW.;  widti,  4  feet. 

Altered  felsite-porphyry.    Vein:  strike,  N.  80°  E. ;  dip,  80°  S. 
width,  10  feet. 

IHoritp  (diabase  '}.     Contains  fibrous  nralitic  hornblende,  which 
may  have  come  from  angite :  chlorite,  enidote,  and  calciteasde 
composition  products.     Vein :  strike,  S.  27°  W. ;  dip,  75°  W. 
width,  4  feet. 

Dioritic   (?)  rock  with  quartz  in  small  grains.     Vein  vertical 
strike,  NW. ;  width,  4  feet. 

Quartz-bearing  hornblende-diorite.     Vein :    strike,  N.  45°  W. 
dip,  86°  SW. ;  width,  7  feet. 

Diorite?  (called  syenite).     Vein:    strike.  NW. ;   dip,  82°  SW. 
width,  10  foet. 

Biotite-gneiag.  A  dike  of  quartz-porphyry  c-uts  therein  at  right 
angles.  Vein  vertical;  strike,  N.62°\v". ;  average  width,  10 
feet. 


Diorite?  (called  syenite), 
width,  5  feet. 


Vein:    strike:  KW. :    dip,  80°  SW.  j 


North  Star  (Sultan  mountain) . 

North    Star    (King    Solomon 
mountain). 


Hanging  wall  white  indistinctly  stratified  rock,  consisting  of 
quartz  and  feldspar — between  a  qnartzitc  and  a  gneiss ;  foot 
wall  decomposed  porphyry.  Vein  vertical  ;  strike,  NE. ; 
width,  6  feet. 

Very  much  decomposed  porphyry.  Vein :  strike,  N.  36°  W. ; 
dip,  65°  SW. 

Greenish  felsitic  rock  (diorite  >).  Vein:  strike,  N.  47°  E. ;  dip, 
74°  NE. :  width,  40  feet. 


Galena  and   cernssite,  with  grav  copper,  rich  in^ilver   (frei- 
bergite). 

"Carbonate"  ore  in  quartz,  with  incrustations  of    ocher,  azn- 
rite,  and  malachite.    Gangue  :  altered  country. 

Massive    freibergite  in  gangne  of  calcite  and  dolomite,  with  a 
little  galena. 


Mixture  of  galena,  freibergit*.  and  chalcopyrite,  with   barita 
between  quartz  layers,  forming  banded  vein  material. 

Freibergite,  galena,  pyrite,  and  chalcopyrite  in  quartz. 
Xreibergite,  pyrite,  and  some  galena  carrying  silver.  . 

Galena,  freibergite,  and  chalcopyrite  carrying  silver,  with  trace 
of  gold. 

Argentiferous    galena,    freibergite,    and  i-halcopyrite.      Quart/ 
gangne. 

Galena  and  barite,  with  stains  of  copper  minerals. 


Mas-iive  argentiferous  galena,  freibergite,  anil  zincblende,  with  a 
little  pyrite. 

Argentiferous  galena  and  cemssite,  with  freibergite. 


a  Trans.  A.  I.  M.  E.,  August,  1882. 


84 


PRECIOUS  METALS. 


Mine. 


LAS  ASIMAB  DISTRICT — COnt'd. 

Philadelphia 

Pride  of  the  West 


Country  rock  and  vein. 


EUKEKA  DISTRICT. 


Adelphi 


Big  Giant. 

Bonanza  tunnel , 


Columbia  . 
Mastodon . 


Sioux  City 

Tom  Moore 

UNCOMPAHUUE  DISTRICT. 


Alabama 


No  specimen.  Called  "  trachyte ".  Vein:  strike,  NW.;  dip,  71° 
S W. ;  24  feet  wide. 

Dark  preen  compact  decomposed  rock,  in  part  breccia.  Undeter- 
minable. Vein:  strike,  NW.;  width,  28  feet 

Quartz-free  plagioclase  rock,  with  crystalline  gronndmass, 
probably  diorite.  Basic  silicate  changed  to  chlorite  and  calcitfl. 
Vein :  strike,  NE. ;  dip,  78°  SE. ;  width,  3  feet. 


White  quartz-porphyry, 
width,  23  fflfct. 


Vein :  strike,  K.  50°  E. ;  dip,  45°  SE. ; 


Porphyrite,  with  biotite,  and  probably  hornblende,  and  a  little 
quartz.  Much  calcite  in  lilms. 

Diorite?    Vein:  strike,  NE. ;  dip,  86°  SE 

Decomposed  greenish  rock  (diorite?).  Vein:  strike,  N.  40°  E. ; 
dip,  70°  SE. ;  width,  200  feet. 

Greenish  decomposed  rock  (diorite?).  Vein:  strike,N.;  dip,  78° 
E. ;  width,  4  feet. 

Greenish  decomposed  rock  (diorite).  Vein  nearly  vertical; 
strike,  NE. ;  width,  00  feet ;  pay  streaks,  9  inches  to  5  feet. 

Greenish  eruptive  roek,  with  porphyritic  crystals  and  included 
fragments  of  red  quartzite.  Vein  :  strike,  NE. ;  dip,  70°  E. ; 
width,  25  feet. 

Alaska I  Diorite  or  diabase  microscopically  similar  to  that  of  the  Adelphi. 

.Vein:  strike,  NE.;  dip,  80°  SE. ;  width,  30  inches. 


Annie  Wood. 


Bonanza. 


Button. 


Maid  of  the  Mist. 


Mammoth  . 


Ked  Cload. 


Hanging  wall  (?)  plagioclase-hornblende  rock;  diorite  (?) ;  foot 
wall  (?)  much  allured  porphyritic  diabase;  groundmass,  crys- 
talline. Vein :  strike,  N.  20°  to  30°  E. ;  dip,  80°  E. ;  5  feet  wide. 


Greenish  felsite-porphyry  much  altered.    Vein:  strike,  N.  65°  E.; 
dip,  80°  SE. 

Light-colored  decomposed  porph\  ry .    Vein :  strike,  N.  20°  E. ; 
dip,  70°  SE. ;  width,  4  feet. 

Plagioclaso  rock ,  with  both  hornblende  and  angitc.    Porphyrite 
ordiabase  (?).    Vein:  strike,  N.  20°  E. ;  dip,  65°  E. 

Greenish  decomposed  porphyry ;  basic.    Vein  :  strike,  N.  10°  E. ; 
dip,  72°  SE. ;  width  on  surface,  30  to  60  feet. 

Too  much  altered  for  determination.    Vein:  dip,  75°  SE. ;  width, 
3  feet 

Red  Rogers i  Greenish  country  rock ;  decomposed  porphyry.   Vein:  strike,  N. 

5u°  E.;  dip,  80°  SE. ;  width,  4  feet. 

Saxon Green  decomposed  porphyry.    Vein:  strike.NE.;  dip,85°  SE.; 

width,  30  to  40  feet. 


Ore  and  ganguo. 


Freibergite ;  a  little  galena,  with  silver  and  some  gold,  in  quartr 
gangue. 

Massive  argentiferous  galena,  with  chalcopyrite  and  freibergite. 


Massive  freibergite,  with  barite  and  some  ohalcopyrite.* 


Freibergite,  argentiferous  galena  and  pyrito,  with  quartz. 

Occurs  in  two  parallel  veins,  ono  carrying  galena,  the  other  frei- 
bergite and  barite. 

Freibergite,  with  some  galena  and  pyrite. 

Massive  argentiferous  galena,  with  layers  of  qnartz  parallel  to 
the  cube  faces ;  zinc  blende,  pyrite,  and  oholcopyrite  also  occur. 

Mainly  galena ;  some  gray  copper. 
Argentiferous  galena  and  zincbleude ;  mussive. 


Argentiferous    galena  and   fivibergite,  with  some  pyrite    and 
chalcopyrite.    Gangne :  quartz  and  feldspar. 

Chiefly  freibergito,  with  some  galena,  and  containing  bismuth-sil- 
ver iu  considerable  quantity. 

Freibergite,  stephanite,  ruby  silver,  sulphide  of  bismuth  with 
chalcopyrite. 


Freibergite  and  chalcopyrite  with  barite. 
found.    Quartz  gangue. 


Galena  and  pyrite  also 
Gaugue : 


Argentiferous  ealena  with  cbalcopyriteand  zinoblende. 
quartz  and  altered  country. 

Argentiferous  galena,  freibergite  and  zinoblende,  with   chalco- 
pyrite and  pyrite.    Gangue  :  quartz  and  altered  country. 

Freibergite,  stepbanite,  ruby  silver,  native  silver,  sulphide  of  bis- 
muth, with  pyrite  iu  quartz  and  altered  country. 

Argentiferous  galena,  freibergite,  zincblende,  chalcopyrite,  and 
pyrite,  with  some  gold  in  qnartz  and  altered  country. 

Freihergite,  stephanite,  ruby  silver,  with  barite  and  qnartz  ;   a 
little  galena. 

Freibergite,  galena,  and  stephanite  (?),  with  some  chalcopyrite. 
Gangne:  qnartz. 


OURAY  COUNTY. 

/ 

Ouray  county  includes  the  northern  and  western  slopes  of  the  San  Juan  mountains,  with  certain  outlying 
groups  belonging  geologically  to  the  same  mass,  and  the  plateau  country  extending  westward  from  thence  to  the 
Utak  line,  which  is  composed  mainly  of  nearly  horizontal  Mesozoic  beds. 

The  development  of  the  precious  metals  has  been  thus  far  confined,  as  might  be  expected,  to  the  eastern  and 
more  mountainous  portion  of  the  county.  In  the  neighborhood  of  Ouray,  which  is  near  the  northwest  limit  of  the 
eruptive  area  of  the  San  Juan  mountains,  erosion  has  exposed  the  underlying  Paleozoic  formations  and  a  small 
area  of  what  is  presumably  Archreau.  The  deposits  of  the  northern  portion  of  the  Uncompahgre  district  occur 
mostly  in  the  sedimentary  beds,  but  in  general  are  more  or  less  closely  connected  with  the  overlying  eruptive  rocks. 
The  veins  belong  more  generally  to  the  metamorphic  type,  although  there  seems  to  be  no  marked  change  in  their 
mineral  constitution.  Mineral  Farm  seems  to  be  a  somewhat  exceptionally  rich  deposit  in  limestone.  In  Sneffles 
district  to  the  west  of  Ouray,  in  Upper  San  Miguel  district,  and  in  Iron  Springs  district  near  Ophir,  to  the  south,  the 
veins,  like  those  of  San  Juan  county,  are  in  eruptive  rocks,  and  stand  at  a  high  angle,  many  of  them,  especially  in 
the  latter  district,  carrying  considerable  gold.  In  the  neighborhood  of  Rico,  still  farther  south,  the  ores  occur  in 
sedimentary  rocks,  in  general  parallel  with  the  stratification  and  with  either  foot  or  hanging  wall  of  porphyry. 
They  are  essentially  silver-bearing,  and  have  a  clay  gangue  material  colored  by  hydrated  oxides  of  iron  and 
manganese. 


Mine. 


UXCOMPAHGRE  DISTBICT. 


Country  rock  and  vein. 


Uegola ;  Blue-gray  crystalline  limestone,  with  chert  segregations.  Quartz- 

poiphyry  is  said  to  occur. 

I>exter j  Hanging  wall   greenish  folnitt>porphyry,  and  shale  below.    Foot 

wall  shale,  and  quartzite  below.    Vein :  strike,  N.  20°  E. ;  dip, 
30°  E.  with  country ;  width,  18  inches. 


Golden  Gate . 
Grand  View  . 


White  quartzite.    Vein  :  strike  N.  20°  W. ;  dip,  80°  AV. ;  width, 
4J  feet. 

Sandstone  and  conglomerate  overlaid  by  eruptive  rock,     Vein: 
strike,  N.  82°  W. ;  dip,  77°  S. ;  18  inches  wide. 


Ore  and  gangue. 


Argentiferous  galena,  chalcopyrite,  and  pyritc,  with  froiberpti- 
and  stibuitt!  (?).  Gangue:  quartz  and  barite. 

Massive  argentiferous  gulena,  native  silver,  stephanite,  zinc- 
blende.  Chalcop\  rite  and  pyrite  are  said  to  occur.  Gangue: 
quartz  and  altered  country. 

Argentiferous  galena,  freiborgite,  chalcopyrite,  and  pyrite  in 
quartzite. 

Pyrito  and  chaleopyrito,  carrying  gold  and  silver,  impregnating 
country  rock. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION. 


85 


Mine. 


UXCOMI'AIIGBK  DISTRICT — COnt'd 

Riverside 

Union 

8XEFFLE8  DISTRICT. 

Potoei 

Terrible 

U.  S.  Depository 

Virginius 


Country  rook  and  rein. 


Green  porphvritic  rock  called  trachyte.     Vein :    strike,  N.  50° 
E.  i  dip,  78°  S. ;  width,  4  fret. 

Gray  porphyritic  rock  called  trachyte.    Vein:  strike,  N.  40°  W. ; 
dip,  80°  S. :  width,  7  feet. 


Wheel  of  Fortune 


Yankee  Boy 

PIOXBRR  DISTRICT. 
Grand  View 


Hope 

Newman 

UPPRR  8AM  MIGUEL  DISTRICT. 

Alto 

Cimmarfon  .................... 


Greenish  fetaitic  rock,  locally  called  trachyte.  Vein :  strike.  NE. : 
dip,  65°  NW. 

Probably  altered  diabase.    Vein :  strike,  N.  80°  W. ;  dip,  85°  S  . . . 

Undeterminable  brecciated  eruptive  rock,  locally  called  trachyte 
Vein:  strike,  N.37°  W. ;  dip,  75°  SW. ;  width,  5J  feet. 

No  specimen  ;  locally  called  trachyte.  Vein:  strike,  N. 32°  W.; 
dip,  80°  SW. ;  width,  4  feet 

Porphyritic  rock  like  that  generally  called  trachyte  in  the  region. 
Vein  :  strike,  N.  5°  W. ;  dip,  60°  \V. ;  width,  5  feet. 

No  specimen  ;  locally  called  trachyte.  Vein:  strike,  y.  85°  W. ; 
dip,  85°  S. 

Hanging  wall  decomposed  porphyry  or  porphyrite;  foot  wall  blue 
fine  grained  dolomite.  Deposit :  dip,  45°  to  72°  NE.,  2  to  14  feet 
thick. 

Hanging  wall  porphyry  (?).  Foot  wall  limestone.  Vein:  dip,  25° 
NE. ;  deposit,  1  to  8  feet  thick. 

Hanging  wall  dark  argillaceous  shale.  Foot  wall  porphyry  or 
porphyrite.  Vein:  dip,  8°  NW.,  6  feet  thick. 

Undeterminable;  called  trachyte.  Dike  of  altered  porphyry(?). 
Vein  :  strike,  N.  75°  W. ;  dip,  70°  If. 


Ore  and  gangne. 


Argentiferous  galena,  with  pyrite  and  a  little  freibergite. 

Argentiferous  galena,  ebalcopyrite,  and  pyrite,  and  some  ste- 
phanitc. 

Freibergitr.  strplianitf.  and  argentiferous  galena,  in  white  quartz 
and  decomposed  country. 

Mainly  argentiferous  galena.    Gangne:  quartz  and  altered  conn  - 

try. 
Argentiferous    galena,  zincblende,   and    freibergite.  with  some 

pyrite. 

Argentiferous  galrna  and  freibergite.    Gangne:  quartz  aud  al- 
tered country  rock. 

Stephauite  and  froibergite.    Gangue :  quartz  and  porphyry. 

Argentiferous  galena  and  zincblende,  with  barite  and  chalcopy- 
rite.    Gaugne:  quartz  and  altered  country. 

Oxides  of  manganese,  carrying  silver,  probably  as  chloride  or 
sulphide. 

Hydrated  iron  and  manganese  oxides,  carrying  silver. 

Iron-stained  clayey  mass,  carrying  silver,  carbonate  of  lead,  and" 
other  minerals. 


Decomposed    rock,    probably    porphyrite    or    diabase, 
strike,  N.22°  E. ;  dip,  75°  SE. ;  width,  3  feet. 


Vein : 


Gold  King Undeterminable.    Porphyry  (?)     Vein  :  strike,  N.  22°  E. ;  dip,  75° 

SE. ;  width,  3  feet. 

N.  W.  H.,jr Greenish  brecciated  undeterminable  eruptive  rock  called  trachyte. 

Vein:  strike,  N.  10°  W. ;  dip,  82°  W. ;  width,  12  feet 


Palmyra 

Pandora  &  Oriental. 

Smuggler 

Summit 


IKON  »rBraa 


Uontoznma. 

Nettie 

Nevada 


Osceola 

Parson 

Pike 

Valley  View . 
What  Cheer  . 


Locallv  called  trachyte.      Decomposed  porphyry.     Vein:  strike, 
N.  35°  W. ,  dip,  65°  NE. ;  width,  4  feet. 

Greenish  undeterminable  rock,  locally  called  trachyte.     Vein : 
strike,  N.  72°  E. ;  dip,  60°  S. ;  width,  10  feet. 

Greenish  undeterminable  breccia,  locally  called  trachyte.    Vein  : 
strike,  N.  18°  W. ;  dip,  65°  W. ;  width,  10  feet. 

Undeterminable  eruptive  rock  locally  called  trachyte.    Vein : 
strike,  NE. ;  dip,  75°  NW. ;  width,  4' feet. 


Crystalline  quartz-porphyry. 
S. ;  width,  4J  feet. 


Vein  :  strike,  E.  and  W. ;  dip,  55° 


White  "siliceous  limestone".  (Porphyry')  Vein:  strike,  NW. ; 
dip,  66°  NE. ;  width,  44  feet. 

Called  trachyte.    No  specimen.    Vein  vertical ;  strike,  NE 

Biotite-porphyrite.    Vein :  strike,  N.  88°  W. ;  dip,  70°  N. ;  width, 
4  feet. 

Fine-grained  very  crystalline  quartz-porphyry.     Vein :  strike,  E. 
aud  W. ;  dip,  60  N. ;  width,  5  feet 

Syenite  or  diorite  (?)  with  a  little  quartz.      Vein:  strike,  N.  15° 
'E. ;  dip,  75°  W. ;  width,  4  feet. 

Called  trachyte.    No  specimen.  Vein,  vertical ;  strike,  NE. ;  dip, 
90° ;  width',  3  feet 

Quartz-porphyry. like  Lincoln  porphyry.  Vein,  vertical;   strike, 
N.40°E.;  width,  4  feet. 


Argentiferous  galena  and  freibergite,  with  barite  and  quartz. 
Several  parallel  veins. 

Argentiferous  galcnn,  freibergite,  chalcopyrite  and  pyrite,  with 
some  free  gold.  Gangue:  light-colored  felsitic  rock,  banded 
parallel  with  walls. 

Gold-bearing  quartz  in  altered  country  rock. 

1  Quartz  impregnated  with  ?alena,  zincblende,  chaleopyrite,  and 
pyrito,  carrying  gold  and  silver.  Gangue :  quartz  and  altered 
country  rock. 

Argentiferous  galena,  with  barite  and  stibnite.  Gangue :  quartz 
and  altered  country. 

i  Auriferous  quartz,  with  pyrite  and  chalcopyrite. 

Native  silver,  stephanite,  argentiferous  galena,  and  zincblende. 
Gangue  :  quartz  and  altered  country. 

Argentiferous  galena,  cernssite,  with  stephanite  and  freibergite. 
Gangue :  quartz  and  altered  country. 

Galena,  ccrussite,  with  some  chalcopyrite,  in  quartz  and  altered 
country  rock. 

Galena,  pyrite,  and  auriferous  iron-stained  quartz. 

Galena,  freibergite,  chalcopyrite.  and  pyrite.  Gangue:  qn.irti 
and  porphyry. 

Iron-stained  auriferous  quartz.  Gangne:  quartz  and  altered 
country. 

Argentiferous  galena,  zincblende,  pyrite,  and  barite.  Gangne: 
quartz  and  altered  country. 

Argentiferous  galena  and  pyrite,  with  a  little  gold,  in  gangue  of 
dolomite  and  quartz. 

Argentiferous  galena  and  cernssite. 

Argentiferous  galena  and  freibergite,  with  chalcopyrite,  pyrite, 
and  zincbleude.  Gangue :  quartz  and  altered  country. 


LA  PLATA  COUNTY. 

La  Plata  county  lies  to  the  south  of  Ouray  and  San  Juan  counties,  and  is  largely  a  mesa  country  formed  of 
approximately  horizontal  Mesozoic  beds,  protruding  through  which  are  the  eruptive  masses  of  the  La  Plata 
mountains  and  the  Sierra  el  Late.  The  coal  horizons  underlie  a  large  portion  of  the  county,  as  well  as  a  portion  of 
western  Ouray,  and  developments  have  been  made  in  the  more  thickly  settled  portions. 

In  the  census  year  its  mines  were  mostly  in  the  condition  of  prospects.  A  schedule  was  obtained  from  only 
one  producing  mine,  the  Comstock,  in  the  California  district,  on  the  west  side  of  the  La  Plata  river,  and  2£  miles 
north  of  Parrott  City.  Its  ore  deposit  occurs  in  a  dike  of  felsite-porphyry  included  in  a  reddish  sandstone  or  quartzite, 
lithologically  resembling  those  of  the  Upper  Carboniferous  of  Park  county.  The  deposit  strikes  north  and  south 
with  the  formation,  dipping  65°  to  the  eastward,  and  is  apparently  an  impregnation  or  alteration  of  the  country 
rock  for  about  6  feet  in  width  near  the  hanging  wall  of  the  dike.  Its  ore  is  auriferous  pyrite  in  a  quartz  gangue, 
with  scattered  spots  of  galena  and  gray  copper.  Specimens  have  been  brought  in  from  an  extremely  interesting 
deposit  of  copper  glance  in  a  coarse  conglomerate  resembling  lithologically  those  which  occur  in  the  lower  portion 
of  the  Triassic  formation  found  to  the  west  of  Dnrango.  A  similar  deposit  is  said  to  occur  in  the  valley  of  the  Rio 
Dolores,  in  the  immediate  neighborhood  of  a  mass  of  eruptive  rock  which  traverses  the  sedimentary  conglomerate. 


86  PRECIOUS  METALS. 

HINSDALE  COUNTY. 

Hinsdale  county  lies  to  the  east  of  Ouray  and  San  Juan  counties,  its  area  being  mainly  covered  by  eruptive 
rocks,  with  some  exposures  of  underlying  Archaean  in  the  valleys  tributary  to  the  Lake  fork  of  Gunnison  river. 
Its  mines  occur  mostly  between  Lake  City  and  the  crest  of  the  range  which  divides  this  county  from  San  Juan. 
In  manner  of  occurrence  of  country  rock  and  minerals  they  resemble  those  of  the  latter.  Exceptionally,  the  country 
rock  of  the  Ohio  Consolidated  mine,  on  Henson  creek,  15  miles  west  of  Lake  City,  is  a  fresh  feldspar-basalt, 
Containing  olivine,  which  is  largely  altered  to  serpentine. 


Mine. 


Country  rock  and  vein.  On'  mid  gaujrue. 


OAI.ENA   DIBTI1ICT. 

Cnlifoinift Porphyrite  (!)     Hnnfrinj>  will  resemblea  decomposed  feleite-por-  .A  rjfcnt  herons  g:ilenu.  IVeibi:rgite.  zincbleude.  ciialcopyrite,  with 

phyry.    Vein:  strike  N.  57°  E.:  dip,  55°  N  w. ;  bonded  at  rue-  '      oalclte  and  rhodocbrocite  ('Tin  quartz  gangne, 
lure,  4  feet  wide. 

Oc«-an  Wave Cray  cniptive.  called  traehyte.    Vein:  strike  UK. :  dip.  80°S.;  Aracntiferoua    galena    and    ireiucrgite:    little    native    copper. 

width.  4  l'(>et.  (Jan;:"!-:  quartz  and  altered  country. 

Ohio  Consolidated |  Foot  wall  fresh  feldspar-basalt,  with  olivine  alleled  to  seipeu-  ,  Freiber;iit<- and  clml<  opvrite.     Ganjiuo:  quartz  and  altered  roitn- 

tine;    hanging  wall    nuieh    altered  basic   rock,   possibly  the  try. 
same.    Vein  :  strike  N.r.°  W. ;  dip,  73°  W. ;  3J  feet  wide,' 

Palmetto -    Gray  diabuse-porphyrite,  with  tendency  to  amygdaloidal  struc-  ("haleopyrite,   atephanite,  and   ruby  silver,   with  some  gold  in 

ture.     Vein:  itrtke  2T.  25°  E. ;  dip,  7;j°  S. ;  4t'e<twide.  qut.rtz  liun^ue. 

.Silver  Cord  Extension '  No  apec.imen  :  locally  railed  porphyry.    Vein  :  at  like  X.  10°  W. ;  ;  Freil  er^ite.  with  native  ailver  and  galena,  chalcopyritc  and  ziuo- 

dip,  85°  E.    No  foot  wall  found.  blende.     Gangue :  quartz,  with  a  little  altered  country. 

UJay&Ute...                             .    Decomposed  undeterminable  rock,  locally  called  trachvte.    Vein:  ;  Freibergito,  galena,  and  chalcopvrite  :  quartz  gansue. 

stiikeNE.:  dip,  74°  (?). 

LAKE   DISTRICT. 

JJellcof  the  West I  Decomposed  light-colored  orthoclaee  rock,  with  little  quartz  ;  lo-  j  Argentiferous    galena,    freibergite,  zincblende,   and   auriferous 

cally  called  trachyte.      Vein:   strike  N.  55°  E.;    dip,  02°  S. ;  ,      cnalcopyrite ;  quartz  gangne. 
width,  18  inches. 

I'ARK   DISTKICT. 

Ine/. !  No  specimen  ;  called  diorite.    Vein  vertical;  strike  N.  34°  E....  Stephanito  and  galena,   with  pyrite.  and  chalcopyrite;  quart/. 

gangue. 


SAGUACHE  COUNTY. 

Saguache  county  comprises  the  head  of  San  Luis  valley,  with  the  slopes  of  the  Saugre  de  Cristo  range,  which 
face  it  on  the  northeast,  and  the  Cochetopa  hills  on  the  northwest,  a  volcanic  mass,  reaching  from  the  southern 
end  of  the  Sawatch  range  to  the  San  Juan  mountains. 

No  working  mines  of  the  precious  metals  are  reported  for  the  census  year.  On  the  western  slope  of  the  Sangre 
de  Cristo,  not  far  from  Hayden's  pass,  occurs  a  rich  deposit  of  red  hematite  iron  ore  in  limestone  (Carboniferous?), 
which  is  worked  by  the  Colorado  Coal  and  Iron  Company,  and  to  which  a  branch  road  has  been  extended  from 
the  Denver  and  Rio  Grande  railroad  above  Poncho  Springs.  Iron  ore  is  also  said  to  occur  on  the  west  slopes  of  the 
Cochetopa  hills,  in  the  valley  of  one  of  the  creeks  tributary  to  the  Gunnison  river. 

KIO  GRANDE  COUNTY. 

Rio  Grande  county  comprises  the  very  uppermost  portion  of  the  valley  of  the  Rio  Grande  and  the  eastern  end 
of  the  San  Jnan  mountains,  which  is  made  up  almost  entirely  of  eruptive  rocks,  said  to  belong  to  the  Tertiary 
volcanics. 

Little  Annie  mine,  in  the  Summit  mining  district,  is  the  most  important  producing  mine.  It  is  situated  about 
28  miles  to  the  southward  of  Del  Norte,  at  the  head  of  Alamosa  creek.  It  is  an  exceptionally  rich  deposit  of  free 
gold  in  quartz  45  feet  in  width  at  the  surface.  The  quartz  is  a  peculiarly  cellular  rock,  and  the  cavities  are 
supposed  to  be  those  left  by  the  leaching  out  of  feldspar  crystals.  The  country  rock  is  probably  an  older  porphyry. 
This  could  not  be  determined  for  want  of  n  specimen ;  but  it  has  been  suggested,  with  considerable  appearance 
of  probability,  that  the  so-called  vein  is  an  altered  porphyry  dike  impregnated  with  mineral. 

GEOLOGICAL  SKETCH  OF  WYOMING. 

The  territory  of  Wyoming  lies  to  the  north  of  Colorado,  having  a  corresponding  area  as  measured  by  degrees 
of  latitude  and  longitude,  but  sel  off  2°  of  longitude  to  the  westward. 

Although  directly  in  the  line  of  the  main  Rocky  Mountain  uplift,  the  larger  portion  of  its  area  is  a  plain  or  mesa 
count)  y.  The  Colorado  range  extends  a  short  distance  north  of  the  boundary  of  that  state,  but  with  a  very  much 
diminished  elevation.  In  the  northwestern  corner  of  the  territory  is  a  considerable  mountain  area,  occupied 
principally  by  the  Wind  River,  Shoshone, and  Big  Horn  ranges,  which  are  connected  with  the  northern  continuation 
of  the  Colorado  range  by  low  east  and  west  ridges,  the  Sweetwater  and  the  Semiiiole  mountains.  In  the  extreme 
northeastern  portion  of  the  territory  a  portion  of  the  Black  Hills  uplift  is  included  within  its  boundaries. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  87 

With  these  exceptions  its  area  consists  of  broad  grassy  valleys  or  Tertiary  mesas,  which  either  form  arid  deserts 
or  are  covered  with  a  somewhat  scanty  growth  of  nutritious  grasses.  But  few  large  streams  are  found  in  the 
territory,  although  within  its  area  are  some  of  the  sources  of  the  three  great  river  systems  of  the  country,  viz,  the 
Green  or  Colorado  river,  which  flows  southward  through  its  center;  the  Snake  Fork  of  the  Columbia,  which  lakes 
its  rise  in  the  northwestern  portions;  and  the  Platte, Cheyenne,  Powder,  and  Wind  rivers,  important  tributaries  to 
the  great  Missouri  River  system.  With  the  exception,  therefore,  of  narrow  strips  of  alluvial  soil  in  the  bottom  lands 
of  these  streams  and  their  tributaries,  it  is  of  little  value  for  agricultural  purposes.  On  the  other  hand,  the  immense 
stretch  of  grassy  plains  available  for  grazing  constitutes  its  great  wealth. 

Our  geographical  and  geological  knowledge  of  the  territory  is  mainly  obtained  from  the  reports  of  the 
Exploration  of  the  Fortieth  Parallel,  whose  field  of  labor  covers  a  narrow  strip  along  its  southern  border,  and  from 
detached  notes  on  the  same  field  made  by  the  Hayden  survey.  The  last  season's  fie^d-work  of  this  survey  (in  1878) 
covered  a  considerable  portion  of  the  western  and  northern  areas  of  the  territory,  but  its  results  are  not  yet 
printed.  («) 

GENERAL  GEOLOGY. — It  is  doubtful  whether  any  portion  of  this  territory  emerged  from  the  surface  of  the  ocean 
during  the  Palaeozoic  and  Mesozoic  eras.  At  the  most,  land  areas,  if  they  existed,  were  confined  to  the  northwestern 
portion,  consisting  of  what  now  constitutes  the  Wind  River  range,  and  possibly  portions  of  the  adjoining  moui.tain 
areas.  The  mountains  of  Colorado  find  their  continuation  in  a  system  of  submerged  reefs  and  small  islands, 
stretching  in  a  direction  a  little  east  of  north  to  the  Black  hills  of  Dakota,  and  branching  off  in  a  northwesterly  and 
westerly  direction  to  connect  with  the  Wind  River  range.  In  this  area  sedimentation,  fed  by  material  derived  from 
the  land  areas  of  Colorado  on  the  south,  of  Utah  and  Idaho  on  the  west,  and  of  Montana  and  the  Black  hills  of 
Dakota  on  the  north  and  east,  went  on  without  any  important  interruption  until  the  close  of  the  Cretaceous.  As 
already  noted  in  Colorado,  there  was  a  probable  continental  elevation  toward  the  close  of  this  period,  resulting 
in  the  partial  inclosure  of  the  basin  which  forms  the  central  portion  of  the  territory,  so  that  its  waters  became 
gradually  fresher,  and  were  finally  shut  oft'  from  all  communication  with  the  ocean.  The  conditions  of  this  period 
were  particularly  favorable  for  the  formation  of  coal,  and  the  upper  portion  of  the  Cretaceous,  wherever  it  outcrops 
throughout  the  territory,  has  been  found  to  yield  an  abundance  of  this  valuable  mineral.  After  the  great 
dynamic  movement  at  the  close  of  the  Cretaceous  large  areas  were  still  beneath  the  surface  of  fresh- water  Tertiary 
seas,  iu  whifeh  deposition  went  on  with  great  activity.  It  is  as  yet  too  early  to  outline  definitely  the  areas  of  these 
different  seas,  but  it  is  known  that  within  the  Tertiary  system  there  exist  important  developments  of  beds  of  the 
Eocene,  Miocene,  and  Pliocene  periods.  The  wealth  of  fossil  remains  of  animals,  fishes,  and  plants  which  have 
been  exhumed  from  these  beds  has  already  given  them  a  world- wide  renown  among  students  of  the  evolution  of  life 
on  the  globe. 

The  surface  changes  during  the  Quaternary  have  been  comparatively  small  as  compared  with  those  of  the 
mountain  regions  adjoining;  and  yet  enormous  masses  of  the  beds  deposited  in  the  Tertiary  era  have  been  swept 
away.  In  the  Wind  River  mountains  a  local  system  of  glaciers  existed  relatively  greater  even  than  those  of 
Colorado,  living  relics  of  which  are  said  still  to  exist  in  the  higher  parts  of  the  mountains.  Of  eruptive  rocks  there 
seems  to  be  a  singularly  small  development  iu  this  great  area.  As  far  as  known,  they  are  mainly  confined  to  the 
Yellowstone  park,  in  the  extreme  northwestern  portion  of  the  territory,  whose  geysers,  generally  considered  as 
intimately  connected  with  recent  volcanic  action,  eclipse  the  hitherto  unrivaled  springs  of  the  volcanic  island  of 
Iceland.  In  the  midst  of  the  Tertiary  plains  of  the  great  Green  River  basin  is  found  a  small  flow  of  leucite-lava,  the 
only  occurrence  of  this  mineral,  which  is  characteristic  of  the  lavas  of  Vesuvius,  hitherto  discovered  on  the  American 
continent.  It  is  not  to  be  wondered  at  that  we  have  but  little  information  about  earlier  eruptive  rocks,  since  so 
much  of  the  area  of  the  country  is  covered  by  sediments  deposited  since  their  eruption  and  the  Arch.-eau  areas  in 
.which  they  might  be  found  are  as  yet  comparatively  unstudied. 

GOLD  AND  SILVER. — As  might  be  inferred  from  the  above  brief  sketch  of  its  geological  structure,  Wyoming 
can  scarcely  rival  its  northern  and  southern  neighbors  as  a  producer  of  the  precious  metals.  Its  actual  resources 
have  as  yet,  however,  been  scarcely  developed,  partly  because  the  broad  plain  areas  oft'er  little  inducement  to  the 
prospector,  and  partly  because  he  has  hitherto  been  debarred  from  the  northern  mountain  areas  by  the  Indian  tribes 
to  whose  reservation  they  belonged.  The  only  discoveries  of  ores  of  these  metals  which  are  known  to  the  writer  are 
confined  to  the  Medicine  Bow  range,  a  northern  oft'shoot  of  the  Colorado  range,  to  the  south  of  the  Laramie  plains ; 
to  the  Sweetwater  and  Seminole  mountains,  a  group  of  hills  running  east  and  west  from  the  northern  end  of  the 
Laramie  hills  to  the  Wind  River  mountains;  and  to  the  mining  districts  near  South  Pass,  at  the  southeastern  end  of 
the  Wind  River  mountains.  From  the  latter  reg'ou  alone  were  returns  obtained  by  the  census  experts. 

The  Arrhajan  nucleus  of  the  Wind  River  mountains  consists  mainly  of  granite,  on  whose  northeastern  flanks 
rest  the  Palaeozoic  and  Mesozoic  formations;  while  on  the  southwest  the  Tertiary  beds  of  the  Green  River  basin 
come  directly  iu  contact  with  it.  At  the  southeastern  extremity  of  the  rauge  the  granites  give  way  to  a  series  of 
schistose  rocks,  prevailingly  gneiss  and  mica-schist,  whose  area  extends  out  for  some  distance  beyond  the  actual 

a  Tho  writer  lifts  been  favored  with  a  glance  at  the  topographical  and  geological  maps  of  this  leport,  from  which  part  of  the  data, 
herein  contained  arc  derived. 


88  PRECIOUS  METALS. 

mountain  uplift.  In  the  foot-hills  of  the  range,  near  the  South  pass,  are  the  California,  Miner's  Delight,  and  Shoshone 
districts,  the  former  near  Atlantic  City,  and  the  latter  near  South  Pass  City.  Mines  were  first  discovered  hore  in 
the  fall  of  1867,  and  the  region  was  the  scene  of  considerable  excitement  in  the  following  year.  Wild-cat  speculation, 
danger  from  the  Indians,  and  other  causes  have  combined  to  prevent  its  proper  development;  so  that,  although  the 
mines  are  now  almost  deserted,  it  would  seem  that  their  abandonment  has  not  been  necessarily  due  to  want  of 
good  ores.  From  the  data  obtained,  they  seem  to  be  mainly  free-milling  gold  ores,  occurring  either  in  quartz  veins  or 
as  impregnations  of  the  country  rock,  which  is  mainly  gneiss  of  both  micaceous  and  hornblendic  varieties.  It 
is  difficult  to  form  a  clear  idea  of  the  exact  geological  relations  of  the  deposits,  but  they  would  seem  to  be  in  some 
respects  analogous  to  those  of  the  Black  hills.  Galena  and  copper  ores  are  also  said  to  have  been  found  in  the 
vicinity,  but  their  exact  location  is  not  given. 

Copper  ores  have  recently  been  developed  near  the  Platte  river  to  the  northwest  of  Fort  Laramie.  From 
the  boundary  of  Colorado  northward  to  the  Platte  river  extends  a  broad  flat  ridge,  known  as  the  Laramie  hills, 
whose  surface  is  made  up  of  Archaean  rocks,  from  which  the  Palaeozoic  and  Mesozoic  beds,  which  originally  covered 
it,  have  been  removed  by  erosion.  From  Laramie  peak,  the  northern  extremity  of  this  ridge,  which  itself  was 
possibly  an  island  in  the  Cambrian  ocean,  an  irregular  reef  of  Archaean  rocks  extended  in  a  direction  a  little 
north  of  east  toward  the  Black  hills.  Portions  of  this  reef,  which  in  Tertiary  times  projected  above  the  water, 
now  form  an  irregular  group  of  hills,  known  as  the  Rawhide  buttes.  At  the  southern  base  of  these  hills,  in  the 
sedimentary  rocks  which  rest  against  the  Archaean,  occur  the  deposits  of  copper  above  mentioned.  The  ore  consists 
of  carbonates,  oxides,  and  silicates  of  copper,  containing  no  silver,  and,  thus  far,  not  sufficient  sulphur  to  make  a 
matte.  To  what  geological  horizon  the  country  rock  inclosing  these  ores  belongs  is  not  ktiown,  nor  the  character 
of  the  deposits ;  but  it  seems  probable  that  they  are  rather  impregnations  of  a  certain  bed  than  a  vein  crossing  the 
stratification. 

COAL  AND  IRON. — The  actual  development  of  coal  in  Wyoming  is  already  very  considerable,  and  its  possibilities 
are  immense.  With  the  exception  of  the  mountain  ridges,  the  entire  area  of  the  territory  maybe  said  to  be  underlaid 
by  the  coal  formation.  Over  a  very  great  portion  of  this  area,  it  is  true,  this  formation  is  so  deeply  buried  beneath 
Tertiary  deposits  that  it  is  practically  unavailable.  On  the  other  hand,  the  coal  formations  are  by  no  means 
absolutely  horizontal  over  all  the  plaincountry,  but  have  been  broughtto  the  surface  by  various  geological  movements, 
so  that  the  actually  known  extent  of  its  outcrops  is  very  great.  The  two  largest  basins  are  those  of  fhe  Laramie 
plains  and  of  the  Green  Eiver  basin.  In  the  former  coal  is  worked  extensively  at  Carbon,  on  the  Union  Pacific  railroad ; 
in  the  latter,  coal  beds  have  been  opened  at  Black  Buttes  and  Point  of  Rocks,  on  the  east,  and  at  Rock  Springs, 
on  the  west  of  a  synclinal  basin  lying  east  of  Green  river,  while  the  outcrops  of  a  second  basin  to  the  west  of 
Green  river  have  been  found  extending  all  along  the  western  borders  of  the  territory  and  beyond  the  line  in  Utah 
from  near  the  head  of  Bear  river,  following  the  valley  of  that  stream  and  of  the  south  fork  of  Snake  river  as  far  as 
the  junction  of  the  latter  with  Henry's  fork,  a  distance,  in  round  numbers,  of  17o  miles.  Outcrops  have  also  been 
found  extending  around  the  northwestern* point  of  Wind  River  range,  at  the  head  of  Gros  Ventre  and  Wind  rivers, 
and  at  various  points  among  the  bays  of  the  Big  Horn  mountains  and  the  Black  hills  of  Dakota.  They  have  also 
been  found  not  far  from  the  copper  mines  to  the  north  of  Laramie  peak.  The  only  actual  working  mines,  however, 
are  those  along  the  line  of  the  Union  Pacific  railroad,  which  are  either  owned  by  or  are  indirectly  under  the  control 
of  that  corporation.  Iron  ore  has  been  discovered  in  immense  masses  in  the  Laramie  hills  at  the  bead  of  Horse 
creek.  This  ore  is  magnetic.  The  specimens  as  yet  tested  have  proved  to  contain  too  large  a  percentage  of  titanium 
to  be  of  marketable  value,  but  it  is  by  no  means  certain  that  a  more  careful  investigation  may  not  discover  beds 
comparatively  free  from  this  injurious  constituent.  A  valuable  deposit  of  remarkably  pure  red  hematite  also  exists 
in  the  Carboniferous  strata  resting  against  Rawlings  peak.  The  ore  was  used  for  some  time  as  a  mineral  paint,  but 
the  mine  has  of  late  years  for  some  unknown  reason  been  abandoned.  Petroleum  is  found  in  the  rocks  of  the 
Cretaceous  formation  at  many  points,  and  oil  of  excellent  quality  for  lubricating  purposes  has  been  obtained  in  small 
quantities ;  but  the  practical  value  of  this  formation  as  an  oil  producer  has  not  yet  been  thoroughly  tested.  At 
various  points  in  the  Tertiary  plains  are  beds  of  dried-tip  lakes  containing  valuable  deposits  of  alkaline  salts.  These 
are  specially  frequent  to  the  north  of  the  Union  Pacific  railroad,  between  the  Platte  and  Green  rivers,  and  in 
one  case  a  deposit  of  solid  sulphate  of  soda  15  feet  in  thickness  has  been  proved.  Their  actual  development  is 
awaiting  the  advent  of  some  enterprising  manufacturing  chemist. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION. 

SWEETWATER  COUNTY. 


Mine. 

Country  rock  and  vein. 

Ore  and  gangne. 

CALIFORNIA  DISTRICT. 

Fine-grained  gneiss.    Vein:  strike.  NE.  ;  dip,  S.  ;  2  to  8  fe«t  wide  . 

Hornbleude-sneiss.    Vein  :    strike,   E.  and  W.  ;  dip.  N.;  width 
irregular,  8  inches  to  12  feet. 

Archaean  schists.    Vein  :  strike,  NE.  ;  dip,  N.  ;  width  irregular, 
8  inches  to  5  feet. 

Amphibolite  and  gneiss.    Vein:  strike,  NW.;  dip,  453S.  ;  width 
irregular,  4  to  16  feet. 

"  Black  granite  ";  no  specimens  ;  probably  gneiss.    Vein:  strike, 
NE.  ;  dip,  W  ;  average  1  foot  thick.    Irregular  on  hanging  wall. 

Gneiss.    Vein  :  strike,  NE.  •  dip  SE  •  1  to  4  feet  wide 

Free  gold  in  quart*. 
Do. 

Gold-bearing  quartz. 
Do. 
Free  gold. 
Do. 

Free  gold  in  quartz  and  decomposed  country. 
Free  gold,  with  little  silver  in  quartz. 
Free  gold  in  quartz. 
Do. 

Do. 

Buckeye  State  

Caribou  

Victoria  

MINERS'  DELIGHT  DISTRICT. 
Hartley 

Compact  dark  gneiss.    Vein  :  strike,  SW.  ;  dip,  S.  ;  6  inches  to  2 
feet  in  width. 

Fine-srraincd  gneiss.    Vein  :  strike,  NE.  ;  dip,  S.  ;   1  to  6  feet  in 
width. 

Gneiss  and  whists.     Vein  :  strike,  NE.  ;  dip,  S.  ;  width,  6  inches 
to  5  feet  in  width. 

Gneiss  and  schists.    Vein  :  strike.  N\V.  ;  dip,  S.  ;  1  to  4  feet  in 
width. 

Apparently  Arcbzan  gneiss.    Vein  :  strike,  NW.  ;  dip,  S.  ;  2  to 

Miners'  Delight 

BHOBHONE   DI8TBICT. 

Cariso  ... 

GEOLOGICAL  SKETCH  OF  THE  BLACK  HILLS  OF  DAKOTA,  (a) 

The  Black  hills  of  Dakota  constitute  a  wooded  island  rising  from  2,000  to  3,000  feet  above  the  treeless  plains 
of  Dakota,  quite  isolated  from  the  main  chain  of  the  Rocky  mountains,  whose  foot-hills  lie  100  miles  further  to  the 
west.  Their  uplift  forms  an  oval  some  120  miles  in  length  by  50  in  extreme  width,  its  longer  axis  having  a  direction 
a  little  to  the  west  of  north.  The  surrounding  plain  or  mesa  country  is  covered  by  practically  horizontal  beds  of 
Cretaceous  and  overlying  Tertiary  formations. 

Their  geological  structure  is  that  of  a  singularly  regular  quaquaversal  having  a  central  nucleus  of  Archaean 
schists,  on  which  rest  beds  of  the  Paleozoic  and  Mesozoic  formations  dipping  away  from  it  in  every  direction, 
the  outcrops  of  the  latter  forming  a  series  of  fringing  reefs,  or  so-called  hog-back  ridges,  which  completely  encircle 
the  island.  The  area  in  which  the  Archaeaa  rocks  are  exposed  occupies  the  eastern  and  higher  portion  of  the  hills, 
and  also  forms  an  oval  some  56  miles  in  length  and  24  in  extreme  width,  its  longer  axis  running  north  and  south. 
The  northwestern  portion  of  the  hills  is  covered  by  nearly  horizontal  beds  of  the  Palaeozoic  formation,  patches  of 
which  are  still  left  in  the  Archaean  area,  while  the  steeper  dips  of  the  quaquaversal  are  found  as  a  rule  only  near 
the  foot-hills. 

The  Archaean  rocks  of  the  Black  hills  are  divided  by  Mr.  Newton  into  two  series,  an  older  and  a  newer 
Archaean,  the  former,  in  general,  occupying  the  southwestern  portion  of  the  oval  area  above  mentioned,  and  the 
latter  (the  newer  Archaean)  the  northeastern  portion.  The  latter  he  considers  to  closely  resemble  the  Huroniau 
of  the  east,  and  it  is  certainly  unlike  any  Archaean  formation  yet  studied  in  the  Rocky  mountains,  except  that 
of  the  Red  Creek  area  in  Wyoming,  (b)  which  was  also  considered  as  corresponding  to  the  eastern  Huronian, 
and  resembles  it  lithologically.  The  older  Archaean  is  also  somewhat  different  from  that  of  Colorado,  in  that  it 
contains  but  little  gneiss.  The  granite  which  occurs  in  it,  however,  would  not  seem  to  form  so  much  of  a 
distinctive  character  from  this  Archaean  as  was  thought  by  Mr.  Newton,  since  it  is  apparently  an  exaggerated  form 
of  the  pegmatite,  which  is  largely  developed  in  Colorado  in  secondary  veins  and  irregular  masses  traversing  the 
gneiss  and  schists.  This  older  Archaean  consists,  according  to  Mr.  Newton,  of  quartzose,  garnetiferous,  and 
ferruginous  mica-schists,  chloritic  schists,  amphibolites,  and  subordinate  gneiss,  with  interlamiuated  veins  of  quartz 
carrying  gold.  In  these  occur  large  masses  of  granite  of  lenticular  shape,  conforming  in  general  with  the 
stratification  of  the  schists,  and  made  up  of  very  large  individuals  of  quartz,  feldspar,  and  mica,  crystalline  in 
structure,  but  not  always  in  complete  crystals.  Tourmaline  crystals  are  quite  common  in  the  granite.  This 
granite  Mr.  Newton  regards,  from  the  fact  that  it  sometimes  incloses  fragments  of  schist  and  has  polished  contact 
surfaces,  as  distinctly  of  an  eruptive  origin,  but  as  erupted  in  pre  Cambrian  times.  The  rocks  of  the  newer  Arclnean 
are,  according  to  him,  not  essentially  different  in  mineralogical  composition,  but  are  characterized  by  a  much  finer 
text,ure.  They  consist  of  micaceous  clay  slates,  siliceous  slates,  hydro-mica  schists,  and  qnartzite.  Quartzite  forms 
an  important  constituent,  often  carries  a  certain  amount  of  mica,  and  occurs  in  powerful  beds  from  50  to  200 
and  sometimes  500  feet  thick.  The  mica-schists  are  often  garnetiferous,  and  contain  also  staurotide  crystals. 

a  The  data  for  this  sketch,  additional  to  that  gathered  by  census  experts,  were  obtained  from  A  Ileport  OH  the  Geology  and  Resources 
of  the  Black  Bills  of  Dakota,  by  Heury  Newton  and  Walter  P.  Jenney,  observations  made  in  1875  and  published  in  1880,  and  from  a  paper 
by  W.  B.  Deverenx  on  "  The  occurrence  of  gold  in  the  Potsdam  formation  ",  Trans.  A.  I.  M.  E.,  February,  1882. 

ti  Geological  Exploration  of  the  Fortieth  Parallel,  vol.  II,  Descriptive  Geology,  page  269. 


90  PRECIOUS  METALS. 

Gneiss  also  occurs,  but  rarely.  To  these  should  be  added,  from  data  furnished  by  the  census  specimens,  a  series 
of  very  fine  phyllites  and  some  actinolite  schists.  Interlaminated  lens-shaped  bodies  of  quartz  are  also  noted 
in  this  series  by  Mr.  Newton,  and  are  by  him  supposed  to  be  auriferous.  Mr.  Jenney  considers  these  quartz  bodies 
as  differing  in  the  two  series,  though  the  reasons  for  this  difference  are  not  apparent.  Both  are  parallel  with  that 
bedding,  aud'neither  traverses  it;  both  carry  gold,  but  those  in  the  older  series  he  considers  interlaininated  fissure 
veins  and  continuous,  and  those  in  the  newer  series  as  segregated  veins  and  not  continuous.  The  enormous  quartz 
bodies  which  have  yielded  the  principal  gold  product  of  this  region  belong  to  the  latter  class. 

Overlying  uncouformably  these  Archaean  schists  is  a  thickness,  in  round  numbers,  of  2,500  feet  of  Palaeozoic 
and  Mesozoic  beds,  which,  according  to  Mr.  Newton,  are  entirely  conformable  within  themselves.  These  consist 
first  of  a  thickness  of  250  feet  of  calcareous  sandstones  and  quartzites,  having  a  conglomerate  with  calcareous 
cement  at  or  near  the  base  and  local  developments  of  glauconite  grains  in  the  upper  part.  In  these  are  found 
well- recognized  fossils  of  the  Potsdam  formation,  which  is  classed  by  Mr.  Newton  as  Silurian,  but  which  it  is  now 
more  common  to  group  under  the  Cambrian  epoch.  Above  the  Potsdam  sandstones  are  pinkish  and  gray  limestones, 
passing  up  by  a  gradual  transition  into  red  and  variegated  sandstones,  in  the  former  of  which  are  found  well-recognized 
Carboniferous  types.  Over  these  are  the  red  Triassic  sandstone  beds,  succeeded  by  variegated  clays  and  marls,  with 
a  little  limestone  of  Jurassic  age  and  coarse  yellow  sandstone,  with  clays  and  shales  of  the  Cretaceous  formation. 
The  thicknesses  given  by  Mr.  Newton  are  690  feet  for  the  Carboniferous  group  and  1,440  feet  for  the  entire 
Mesozoic  system.  The  striking  features  in  this  series  of  deposits  are  the  apparent  absence  of  representatives  of 
the  formations  included  between  the  Cambrian  and  Carboniferous  and  the  relative  thinness  of  the  entire  series  as 
compaied  with  sections  found  in  other  parts  of  the  country.  The  latter  fact  is  less  surprising  when  it  is  considered 
that  the  tendency  of  the  Rocky  Mountain  deposits  has  been  observed  to  be  a  thinning  out  toward  the  east,  and 
that  the  Black  hills  were  an  island  at  least  100  miles  east  of  the  Archaean  shore-line.  Whether  the  apparent  gap 
in  the  series  signifies  that  there  was  actually  a  cessation  of  deposition  during  Silurian  and  Devonian  times,  or 
whether  representatives  of  these  formations  exist  but  have  not  yet  been  detected,  is  a  question  that  can  only 
be  definitely  determined  by  far  more  detailed  studies  than  have  yet  been  made. 

The  geology  of  the  Black  hills  is  of  singular  interest,  not  only  to  the  general  but  to  the  economic  geologist, 
and  the  facts  already  obtained  show  that  its  history  has  been  a  remarkably  varied  one.  According  to  Mr.  Newton, 
there  is  evidence  that  the  newer  Archseanis  unconfonnable  to  the  older;  in  other  words,  that  dynamic  movements 
took  place,  and  land  existed  here  which  was  acted  on  by  erosion  before  the  close  of  the  Archaean.  The  conglomerate 
at  the  base  of  the  Potsdam  bears  unmistakable  evidence  of  having  been  a  beach  or  shore  formation,  and  shows 
that  new  land  appeared  at  the  close  of  the  Archaean,  while  the  comparatively  horizontal  position  of  the  Potsdam 
and  Carboniferous  beds  in  elevated  portions  of  the  hills  seems  to  indicate  a  gradual  subsidence  during  the  Cambrian, 
which,  if  the  Devonian  be  really  wanting,  must  have  been  followed  by  a  sufficient  elevation  to  prevent  the  sediments 
of  that  period  covering  its  area.  This  elevation,  however,  must  have  been  of  such  a  gradual  character  that  the 
formations  were  not  disturbed,  inasmuch  as  the  Carboniferous  beds  were  deposited  with  perfect  conformity  on  the 
Cambrian.  At  the  close  of  the  Cretaceous  the  area  of  the  hills  was  again  lifted  above  the  sea  and  a  second 
conglomerate  deposited  round  its  shores.  Erosion  during  this  time  removed  a  large  portion  of  the  Mesozoic  and 
Palaeozoic  beds  to  form  the  surrounding  Tertiaries ;  and  that  elevation  has  gone  on  since  Tertiary  times  seems  to 
be  proved  by  the  evidence  of  conglomerate  beds  more  recent  than  the  Tertiary,  which  exist,  according  to  Mr.  Jenney, 
300  feet  above  the  present  stream  beds,  and  are  made  up  of  bowlders  of  the  Archaean  and  other  rocks  from  the 
interior  of  the  hills.  These  gravels  or  conglomerates  Mr.  Jenney  regards  as  quite  distinct  from  those  of  the  present 
stream-beds,  and  as  probably  dating  back  to  the  close  of  the  Glacial  epoch.  There  are  thus  four  different  ages  of 
gravel  formations,  all  of  which,  except  possibly  the  third,  have  been  proved  to  be  gold-bearing : 

First.  The  Potsdam  conglomerate. 

Second.  That  at  the  close  of  the  Tertiary. 

Third.  That  at  the  close  of  the  Glacial  period. 

Fourth.  The  recent. 

Of  eruptive  or  igneous  rocks,  of  which  there  are  abundant  outbursts,  especially  in  the  northern  portion  of  the 
hills,  where  the  richest  mineral  deposits  have  hitherto  been  found,  Mr.  Newton  recognizes  only  those  of  Tertiary 
age.  It  seems  probable,  however,  that  had  not  his  untimely  death  cut  short  his  observations  a  further  study  might 
have  led  him  to  modify  this  opinion.  Mr.  Caswell,  to  whom  the  specimens  of  eruptive  rock  were  submitted  for 
microscopical  examination,  says  himself  that  in  several  cases  he  would  have  classed  the  rocks  as  quartz  or  feldspar- 
porphyries  had  not  their  geological  relations,  as  described  to  him,  forbidden  it.  Among  the  census  specimens  are 
some  which  undoubtedly  belong  to  these  types.  They  are  the  rocks  which  are  described  by  Mr.  Devereux  as 
breaking  in  dikes  through  the  Potsdam  conglomerate  and  spreading  out  over  its  surface  in  the  neighborhood  of 
Lead  City.  Moreover,  the  structural  relations  of  the  eruptive  masses  which  form  many  of  the  prominent  peaks, 
and  which,  according  to  Mr.  Newton,  have  uplifted  the  surrounding  sedimentary  beds,  belong  rather  to  the  type  of 
earlier  intrusive  eruptives,  analogous  to  the  laccolitic  bodies,  than  to  the  Tertiary  volcanics,  which  as  a  rule  have 
flowed  out  on  the  surface  without  exercising  any  considerable  disturbing  influence  on  the  sedimentary  beds  through 
which  they  have  passed. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  01 

To  the  economic  geologist  the  most  interesting  fact  in  the  geology  of  this  region  is  the  definite  date  given  to 
the  formation  of  the  gold  deposits.  The  Potsdam  conglomerate  is  in  places  an  actual  placer  deposit  formed  on  the 
beach  of  the  Cambrian  ocean  from  the  debris  of  veins  at  present  \vorked  in  the  Archa-an.  The  gold  of  the  Black 
hills  is  therefore  distinctly  of  Archa-an  age.  Mr.  Devcrenx  also  recognizes  a  probable  secondary  deposition,  which 
he  considers  as  probably  resulting  from  chemical  solution  of  gold  contained  in  the  Potsdam  conglomerate  and 
redeposited  in  the  underlying  schists.  He  also  seems  to  consider  the  deposition  of  certain  silver-bearing  ores  in  the 
neighborhood  of  Bald  mountain,  a  region  traversed  by  bodies  of  porphyry  in  the  forms  of  dikes  and  sheets,  which 
occur  in  the  qnartzite  adjoining  these  bodies,  as  dependent  on  the  eruption  of  the  porphyry.  If  the  section  which 
he  gives  of  the  region  in  the  neighborhood  of  Dead  wood  gulch  be  correct,  the  porphyry  must  be  of  subsequent 
date  to  the  erosion  of  the  Cretaceous  and  Palaeozoic  rocks,  and  therefore  probably  post-Cretaceous. 

ORE  DEPOSITS. — The  most  characteristic  ores  of  the  Black  hills  are  auriferous  pyrites,  now  almost  completely 
oxidized,  impregnating  lenticular  masses  of  quartz,  and  portions  of  the  adjoining  schist  in  the  newer  Archaean  of 
Newton.  Owing  to  the  decomposed  condition  of  the  rock  and  its  freedom  from  injurious  metallic  combinations 
these  ores  are  so  exceptionally  easy  of  amalgamation  in  the  stamp-mill  that  they  yield  a  profitable  return,  even 
when  carrying  only  from  $4  to  $G  per  ton  in  gold.  These  deposits  have  been  mainly  developed  in  the  extreme 
northern  portion  of  the  Archaean  area  at  the  head  of  the  Wliitewood  gulch,  in  the  vicinity  of  Lead,  Central,  and 
Dead  wood  cities.  The  country  rock  here  consists  of  fine-grained  mica-schists,  argillites,  or  phyllites,  with  numerous 
interlaminated  lenticular  bodies  of  quartz  parallel  with  the  stratification,  which  has  a  prevailing  northwesterly 
strike  and  a  dip  of  from  50°  to  75°  to  the  northeast.  The  ore  belts  are  from  40  to  200,  300,  and  even  500  feet 
in  width,  and  consist  of  impregnations  of  these  quai'tz  masses  and  portions  of  the  adjoining  country  rock  with 
iron  oxide,  resulting  from  the  decomposition  of  pyrites  carrying  fine  gold.  In  these  belts  are  barren  streaks  or 
"horses"  of  country  rock  and  dikes  or  bodies  of  what  is  locally  called  porphyry.  It  is  evident  that  these  deposits 
have  none  of  the  characteristics  of  a  true  fissure  vein,  though  they  are  none  the  less  valuable  on  that  account.  It 
is  probable  also  that  the  individual  ore  bodies,  or  lenses,  arc  of  limited  extent  both  horizontally  and  vertically,  or, 
as  Mr.  Jenney  says,  not  continuous.  This  fact  is  not  necessarily  derogatory  to  the  deposits  as  a  whole,  since,  while 
one  lens  may  pinch  out,  another  may  be  found  contiguous,  though  not  exactly  in  the  same  plane.  Moreover,  in 
spite  of  the  popular  delusion  in  favor  of  fissure  veins  extending  to  the  center  of  the  earth,  all  known  facts  go  to 
prove  that  all  ore  bodies  are  limited  in  extent,  the  difference  between  one  and  another  being  merely  in  the  extent 
of  the  limit.  Horizontally  the  limit  is  easily  traced,  although  in  depth  it  is  sometimes  beyond  the  present  reach 
of  practical  mine  development. 

Another  important  source  of  gold  is  the  cement  or  Potsdam  conglomerate,  which,  though  its  ore  is  milled  in  the 
same  manner  as  the  vein  material,  is  in  fact  an  ancient  placer  deposit.  It  is  only  of  local  extent,  is  of  varying 
thickness,  and  is  made  up  of  rounded  and  angular  fragments  of  quartz,  hematite,  and  Archaean  schists,  often 
with  ferruginous  cement,  and,  according  to  Mr.  Deverenx.  carries  free  gold,  distributed  in  an  exactly  analogous 
manner  to  that  found  in  modern  placers.  In  many  cases  the  cement  deposit  is  worked  as  a  horizontal  vein,  while  a 
vertical  vein  is  described  as  occurring  immediately  beneath  it.  Whether  Mr.  Devereux  would  consider  all  these 
vertical  veins  as  instances  of  later  deposition  is  not  known  to  the  writer. 

In  mines  reported  from  the  Bald  Mountain  district,  at  the  head  of  the  Whitewood  gulch,  the  reports  show  a 
different  class  of  deposits,  which  consist  of  chlorides  of  silver  and  iron  oxide,  carrying  gold,  impregnating  the  quai  tzite 
strata  to  a  thickness  of  several  feet.  These  are  probably  the  deposits  which  Mr.  Devereux  considers  as  a  later 
formation,  and  connected  with  the  porphyry  outbreaks.  No  specimens  of  porphyry  were  returned  by  experts,  but 
the  district  is  apparently  in  the  neighborhood  of  Terry's  peak,  the  rock  of  which  Mr.  Caswell  reports  as  a  granitic 
rhyolite,  with  a  completely  crystalline  grouudmass,  closely  resembling  granite-  or  felsite-porphyry. 

In  the  Bear  Butte  district,  10  or  12  miles  to  the  eaSt  of  Deadwood,  irregular  deposits  of  argentiferous  galena 
and  cerussite,  with  oxides  of  iron  carrying  both  gold  and  silver,  occur. in  limestones  and  quartzites,  sometimes 
parallel  to  the  stratification,  and  again  ciossing  it,  Gold  is  also  obtained  from  a  conglomerate  or  breccia  largely 
made  up  of  fragments  of  what  is  apparently  felsite  porphyry.  The  geological  relations  of  this  class  of  deposits 
are  not  clear. 

In  Penniugtou  county,  in  the  central  portion  of  the  hills,  free-milling  gold  ore  is  found  in  Archaean  rocks  in  the 
Rockford,  Cross,  and  Newton  Forks  districts;  and  to  judge  from  the  specimens  of  country  rock  sent  in  they  occur 
apparently  in  the  same  Archaean  formation  as  that  of  the  Whitewood  district,  although,  according  to  Mr.  Newton's  map, 
a  portion  at  least  of  these  mines  would  be  included  in  the  older  series.  It  is  to  be  noted,  however,  that  the  geological 
outlines  of  the  map  are  confessedly  imperfect,  owing  to  the  fact  that  Mr.  Newton's  material  had  to  be  worked  up 
by  another  hand  than  his  own.  In  the  Cross  district  the  ore-body  seems  to  be  the  impregnation  of  a  mass  of 
actiuolite-biotite  schist,  instead  of  quartz,  included  within  the  mica-schist  country  rock.  It  is  to  be  noted,  however, 
that  in  these  districts,  while,  according  to  the  census  schedules,  the  formation  strikes  nearly  north  and  south,  its 
dip  in  the  Kockford  and  Cross  districts  is  to  the  eastward,  and  in  the  Newton  Forks  district  to  the  west. 

In  Custer  county,  still  farther  south,  are  the  Cole  and  Custer  districts:  in  which  the  same  lenticular  masses  of 
quartz,  carrying  free  gold,  occur  in  mica-schists.  Both  these  districts  are  included  in  Newton's  older  Archo-an  area. 
The  specimens  of  country  rock  sent  in  are  micaceous  schists,  carrying  considerable  quartz,  and  sometimes 


92 


PRECIOUS  METALS. 


garnetiferous,  while  the  ore-bodies,  in  addition  to  the  quartz,  are  sometimes  amphibole-schists,  and  in  ono  case 
consist  entirely  of  fibrous  tremolite.  Associated  with  the  gold  is  frequently  a  little  silver.  The  prevailing  strike 
is  here  also  nearly  north  and  south,  and  the  dip  to  the  westward. 

Three  miles  to  the  northwest  of  Custer  City  is  a  mica  mine,  in  one  of  the  bodies  of  granite  described 
by  Mr.  Newton.  In  its  general  character  it  resembles  the  pegmatites  of  Colorado,  but  the  size  of  the  individual 
constituents  is  actually  gigantic,  and  the  association  of  minerals  is  somewhat  remarkable.  The  data  are  not 
sufficient  to  determine  the  exact  geological  relations  of  the  rocks.  The  foot  wall  of  mica-schist  strikes  north  and 
south,  and  dips  40°  to  the  westward.  Above  this  a  thickness  of  four  feet  is  worked  for  mica',  which  occurs  in  lar<;e 
sheets  over  a  foot  in  diameter,  usually  nearly  perpendicular  to  the  foot  wall.  Specimens  from  the  zone  next  above 
the  mica  show  albite  (var.  clevelandite),  labradorite,  beryl  in  crystals  2  to  3  inches  in  diameter,  and  a  lithia-mica 
in  small  leaves.  Above  this  is  pure  milky  quartz  of  great  thickness,  said  to  extend  to  the  top  of  the  hill,  over 
100  feet  above  the  vein.  Whether  these  deposits  prove  of  economic  value  or  not,  a  visit  to  it  would  evidently  be 
fruitful  in  interesting  results  to  the  mineralogist. 

PLACER  DEPOSITS. — The  placer  deposits  of  the  Black  hills  are  apparently  of  great  extent  and  richness;  but, 
except  those  immediately  adjoining  the  beds  of  the  present  streams,  which  are  largely  worked  out,  they  have  as  yet 
proved  of  little  practical  value,  owing  to  the  difficulty  of  procuring  a  sufficient,  supply  of  water.  As  already  stated, 
Mr.  Jenney  makes  four  different  ages  of  gravel  deposits.  The  earliest,  or  Potsdam  conglomerate,  is  worked  as  a 
deep  mine,  and  its  ore  is  regularly  crushed  in  the  stamp-mills.  Of  the  pre-Tertiary  conglomerate  no  data  are 
available  as  to  its  contents  in  gold.  It  occurs,  according  to  Jenney,  under  the  Miocene  beds  at  the  mouths  of 
Spring  and  Kapid  creeks,  forming  a  bed  6  feet  in  thickness,  made  up  ot  bowlders  of  granite,  trachyte,  slate, 
quartzite,  and  quartz.  Mr.  Jenney  says  the  glacial  deposit  which  occurs  sometimes  300  feet  above  the  present  bed 
of  the  creek  has  been  proved  to  be  rich  by  actual  test,  but  cannot  be  worked,  owing  to  the  want  of  a  sufficient 
head  of  water.  The  recent  deposits  of  the  present  canons,  according  to  data  furnished  by  the  census,  have  been 
worked  principally  in  the  Archa3an  area,  and  have  an  average  depth  of  from  4  to  30  feet.  Mr.  Devereux  gives  some 
interesting  facts  concerning  the  placer  deposits  of  Deadwood  and  its  tributary  gulches.  According  to  him,  these 
are  formed  in  part  from  the  disintegration  of  the  Potsdam  conglomerate  bed  and  in  jmrt  from  the  actual  wearing 
away  of  the  quartz  deposits  in  the  Archasan,  which  accounts  for  their  exceeding  richness;  the  placers  of 
Black  Tail  gulch  were  entirely  derived  from  the  disintegration  of  the  cement,  as  the  Archaean,  at  the  head  of  the 
gulch,  has  not  been  exposed  to  erosion  in  recent  times.  To  account  for  the  known  superior  fineness  of  placer  gold 
over  that  in  veins,  he  assumes  that  the  chemical  agencies  to  which  the  gold  has  been  subjected  since  it  was  liberated 
from  the  vein  have  acted  more  energetically  on  the  silver  than  on  the  gold.  To  prove  this  he  shows  from  actual 
figures  that  while  the  average  fineness  of  the  gold  from  five  different  veins  was  0.830,  gold  from  the  placers,  which 
would  have  resulted  from  the  disintegration  of  these  veins,  averaged  about  0.900,  and  that  the  small,  thin  pieces 
of  gold,  which  had  proportionately  greater  surfaces  than  the  coarser  particles,  were  finer  than  the  latter. 

The  other  minerals  of  economic  importance  found  in  the  Black  Hills  region  are  beds  of  gypsum,  which  occur 
in  the  Triassic  formation,  and  of  coal,  which  is  mined  in  the  Cretaceous  beds  to  the  northwest  of  the  hills. 

LAWRENCE  COUNTY. 


Mine. 


Country  rock  and  remarks. 


Ore  and  gangue. 


WHITKWOOD  DIBTBICT. 


Badger !  Hanging  wall  felsitic  rock  with  stratified  appearance,  probably 

eruptive.    Foot  wall  mica-schist,  with  some  chlorite.    Ore  belt 
vertical.    Strike,  NW.,  200  feet  wide;  capped  by  conglomerate. 


Black  Tail. 


Caledonia. 


Champion  , 


Dead  wood-Terra. 

Esmeralda 

Fairview 


Father  De  Smet 


Flora  Bell  . 


Giant  &  Old  Abe  . 


Goldfinch. 


Conglomerate  (cement  deposit)  of  fragments  of  Archsean  schist. 
Compact  felsite  overlying  conglomerate.  Ore  body,  horizontal, 
H  feet  I  hick. 

Hanging  wall  phyllite,  with  pyrite  and  gamet.  Foot  wall  mica- 
schist  wiih  rbloritio  layers.  A  felrtite  occurs  whose  relation  is 
not  clear.  Strike.  N.  0°  W. ;  dip,  51°  K.  (I);  twoore  belts,  oue40 
feet,  the  other  182  feet  wide. 

Cap  and  hanging  wall  felsite-porphyry.  Foot  wall  calcareous 
quartzite.  Horses  in  vertical  p;irt  of  vein  composed  of  car 
bonates  ofiron.  lime,  etc.  Strike  of  formation,  NE. ;  dip,  75°  E. ; 
ore  belt,  35  feet  wide. 

Hanging  wall  chlorite-schist  with  garnet.  Foot  wall  mica-slate 
formation.  Stiike,  NW.;  dip,  50°  to  75°  HE. 

Probably  Archiean.  No  specimens.  Overlaid  by  conglomerate 
(cement). 

Archaean  overlaid  by  conglomerate.  Strike,  NW. ;  dip,  50"  to 
75°  NE. ;  cement,  20  feet  thick;  ore  belt,  200  feet  wide  ;  felsite 
(f),  above  the  conglomerate. 

Chloritic  schists.  Strike,  NW. ;  dip,  50°  to  73°  NE. ;  ore  belt, 
150  liet  wide,  with  horses  of  barren  rock. 

Phyllite  on  hanging  wall.  Altered  schist  on  foot  wall.  Horizon- 
tal conglomerate  capped  by  felsite  (?)  above.  Strike,  NE. ;  dip, 
86°  W. 


Archa?an   schists  impregnated  "with  iron. 
50°  to  76°  NE. ;  ore  belt,  60  feet  wide. 


Strike,  NW. ;  dip, 


Quartz  conglomerate,  overlaid  by  fine-grained  Potsdam  sand- 
stone; quartzite  (?)  below. 


Free-milling  auriferous  quartz. 
Free  gold  in  conglomerate. 


Pyritiferous  chloritic  schists  carrying  gold.    Chlorite  apparently 
comes  from  actinolite. 


In  part  steeply  inclined  beds,  in  part  horizontal  beds  resting  on 
upturned  edges  of  Archajan,  overlaid  by  porphyry. 

Ferruginous  quartz  carrying  gold  and  a  little  silver  scattered 
through  a  belt  of  Arcbfeau,  250  feet  wide. 

Free  gold  in  horizontal  cement  deposit,  and  segregated  quartz 
lenses  in  schists  be-low. 

Gold-bearing  cement  and  quartz  lenses  in  iron-stained  mica- 
schist. 

Quartz  lenses  and  altered  schists,  with  pyrite ;  gold-bearing. 
Gold-bearing  cement  and  schist  impregnated  •with  qnartz. 


Ferruginous  gold-bearing  qnartz,  with  a  little  pyrite,  impregnat- 
ing schists. 
Cement  5  to  6  feet  thick,  carrying  free  gold. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION. 

LAWRENCE  COUNTY— Continued. 


93 


Mine. 


Counti y  rock  and  remarks. 


WIIITKWOOD  DISTRICT— COllt'd. 

Golden  Gate, Fine-grained  mica-schists.    Strike,  NW.;  dip,  50°  to  75° NE. ;  ore  | 

belt,  25  feet  wide. 


Golden  Terra 


Gopher 


Great  Eastern  . 


Mica-slate  on  hanging  wall.  Mica  schist,  rich  in  quartz  and  mi- 
croscopic ore  grain*,  on  loot  wall.  Strike,  NW.  ;  dip,  50°  to  75° 
NE.  ;  010  bolt  300  feet  wide,  with  "porphyry  "dikes  and  horses 
of  slate. 


Fine-grained  compact  mica-schist. 
.NE.  ;  ore  belt  (iO  feet  wide. 


Strike,  NW.  ;  dip,  50°  to  75° 


Conglomerate  of  quartz  and  some  schist,  overlaid  by  quartz-por- 
phyry.   Dip,  15°  E.  ;  3  feet  thick  ;  resting  on  schists. 

Hidden  'Preasure Conglomerate  of  quartz  and  schist  fragments ;  horizontal.   Thick- 
ness, 20  ieet  to  nil.     Felsite  above,  Archaean  below. 

Highland Archajan  schists.     Argillite,  on  foot  wall ;  lenticular  bodies  of  fel- 

|      site  (!)  paialh  1  with  the  formation.    Strike,  NW.;  dip,  50°  to  75° 
NE. ;  ore  belt  550  feet  wide,  less  felsite  bodies. 

High  Lode Conglomerate,  resting  on  fine-grained  Archsean  schists,  overlaid 

by  Potsdam  sandstone.     Horizontal ;  8  feet  thick. 

Hoiiiestake Archjeun  schists  and  porphyry  (?)  bodies.    Strike,  N.  10°  to  38° 

W. ;  dip,  51°  E. ;  ore  belt  40  feet  wide. 


Loaella 


OtoCash 


1'eccho 


Portland 


Conglomerate,  resting  on  Archaean,  overlaid  by  sandstone. 
305  E.  ;  7  feet  thick. 


Dip, 


Felsite-porphyry. 
wide. 


Strike,  NW.  ;  dip,  30°  NE.  ;  ore  belt  150  feet 


Conglomerate,  capped  bv  felsito  and  resting  on  Archamn  schists. 
Strike  of  latter,  N.  5°  W. 

Quartzitic  sandstone  (Potsdam?).  Strike,  N  W. ;  dip,  8°  SW. ; 
deposit,  a  nearly  horizontal  bed  and  a  vertical  vein  below.  Hor- 
izontal vein,  7  feet  thick;  vertical;  strike  SW.,  5  feet  thick. 

Rattler  Hanging  wall  quarllite-schist,    foot  wall  mica-schist.     Strike, 

NW. ;  dip,  75°  NE. ;  40  feet  wide, 

.iviiin Archawn  schists.     Ore  belt  38  feet  wide;  strike,  NE.;  dip,85°NW. 

Sir  Roderick  Dim !  Chloritio  schists  and  mica-slates.    Ore,  lenticular  mass ;  dip,  85° 

|      NW. 

Snowstorm * 


Fine-grained  calcareotw  sandstone  above,  quartzitic  schist  below. 
Deposit,  horizontal  :  3  feet  thick. 


BEAU  BUTTK  DISTRICT. 


Carter     Mica-schist,  with  needles  of  decomposed   hornblende.    Strike, 

NW. ;  dip,  85"  W. ;  ore  belt,  100  feet  wide. 

CliTiuout !  Fossiliferons  limestone  on  hanging  wall.      Vein  vertical ;  strike, 

NE. ;  40  feet  wide. 


HI  Refugio 


Quartzito.    Strike,  NE. ;  dip.  15°  SE.  Ore  bodies  irregular,  follow- 
ing stratification ;  average,  2  feet  thick. 


Escoudido  .....  ................    Earthy  limestone.    Deposit:  dip,  80°  E.  ;  Sfectwide  ............. 

Florence  .......................  i  Ferruginous  quartzito  (Potsdam?).    Horizontal;  irregular  bodies 

following  stratification  ;  2J  feet  thick. 

Hoodoo    .......................    Conglomerate  of  felsite  and  stratified  rocks  ;  explored  to  a  depth 

of  25  feet 

Keystone  ......................  '  Porphyry,  with  little  quartz  :  large  pink  orthoclase  crystals  ;  no 

mica  or  hornblende;  called  "  porphyritic  conglomerate". 

MenittNo.2  ..................  •  Qnartzite  (Potsdam).    Dip,  35°  E.  ;  deposit,  7  feet  thick. 

Oro  Fino  .......................  j  Conglomerate  of  schist  fragments,  with  ferruginous  cement  ...... 

Kicb  ...........................  |  Breccia,  or  conglomerate  of  porphyry  fragments.     Dip,  S.  and  E  . 

Sitting  I'.ull  ....................    Qnartzite  (Potsdam).    Dip,  20°  SE.  ;  deposit,  irregular  bodies  fol- 

,    lowing  stratification. 

Union  Hill  .....................    Conglomerate  or  breccia  of  felsite-porphyry 


Washington  ...................    Qnai  tzite  (Potsdam).    Deposit,  irregular  following  stratification  ; 

horizontal,  1  to  8  feet  thii-k. 

Yellow  Jacket.. 


Foot  wall,  mica-schist;  hanging  wall,  indistinctly  schistose  rock. 
Strike,  N  W. ;  dip,  20°  S\V. ;  ore  body  3  feet  thick  following  the 


foimatifin. 


Ore  and  gangue. 


Quart/,  and  schists,  with  little  pyrite  ;  gold-bearing. 
Ferruginous  qnartz,  with  little  pyrite  in  slate. 


Lenses  of  qnartz  and  decomposed  schists;   gold-bearing,  with 
little  pyrite. 

Free  gold  in  cement. 
Free  gold  in  cement. 

Ferruginous  quartz  and  schist,  with  little  pyrite ;  gold-bearing. 

Free  gold  in  cement. 

Ferruginous  quartz  and  schist,  with  little  pyrite,  carrying  free 
gold. 

Free  gold  in  cement. 

Gold-bearing  hematite  ami  limonlte  in  quartz. 

Free  gold  in  cement,  and  gold-bearing  qnartz  and  schists  in 

Archcean. 
Qnartzite,  impregnated  with  horn-silver,  iron  oxide,  and  some 

gold. 

Ferruginous  gold-bearing  quartz. 

Quartzose  iron-stained  masses,  carrying  gold. 
Lenses  of  qnartz  and  pyrite,  carrying  gold. 

Qnartzose  mass,  impregnated  with  gold  and  chloride  of  silver. 


Lenses  of  quartz,  impregnated  with  oxide  of  iron,  and  carrying 

gold. 
Siliceous  hematite,  quartz,  chalcedony,  ocher,  and  in  part  earthy 

limestone,  carrying  gold  and  silver. 
Gold-  and  silver-bearing  galena,  altered  to  cernssite ;  crystals  of 

pyromorphite  and  wulfenite. 
Galena,  pyrite,  and  zincblende,  carrying  silver. 
Pyrolusite,  ocher,  and  siliceous  hematite  impregnating  qnartzlte, 

carrying  silver. 
Frea  gold  in  conglomerate. 

Quartz-bearing  porphyry,  impregnated  with  auriferous  pyrite*. 

Argentiferous  galena,  limonite,  and  ocher,  with  little  gold. 

Free  gold  in  cement. 

Free  gold  in  conglomerate,  with  ferruginous  cement. 

Galena  and  siliceous  hematite,  with  carbonate,  carrying  gold  and 

silver. 

Country  rock,  stained  with  oxide  of  iron,  and  carrying  gold. 
Galena,  carrying  gold  and  silver. 

Cernssito,  carrying  silver  and  some  gold  in  qnartzose  mass. 


PENNINGTON  COUNTY. 


liOCKKOEl)   DISTBIOT. 

Alta  Hanging  wall  greenish  decomposed  mica-schist.  Foot  wall  dark 

plijllito.  Strike,  N. ;  dip,  45°  E. ;  ore  belt,  100  feet  wide. 

California i  Chloritic  mica-schist.    Strike,  N 

Kvangelino |  Silieeot.s  schists.  Strike.  N.  and  S. ;  dip,17°E.;  ore  belt,  40  feet 

wide. 

CBOBS  DIBTHICT. 

Crow* 

Quiney  and  Little  Grace 

NKWTOX   FOURS  DISTRICT. 

King  Solomon 


Quei-nlier 

Koyal  [ivngal  Tiger. 


Mica-schist.   Strike,  N.  17°W.:  dip,85°E.;  ore  belt,  100  feet  wide 
Siliceous  mica-schist.    Strike,  N.  18°  W. ;  dip,  85°  E. ;  ore  belt, 

90  feet  wide. 

Light-colored  phyllites,  garnetiferonson  foot  wall.   Strike,  If.  15° 

W. ;  dip,  fc8°  W. 
Fine-grained  mica-schist.  Strike  N.  and  S. ;  dip,  45°  W. ;  ore 

belt  10  feet  wide. 
No  specimen  ;  nppareutlvsarae  asabovemine.  Strike,  N.  and  S. : 

dip,  85°  \v. ;  ore  belt  10  feet  wide. 


Quartz  and  altered  schist,  carrying  free  gold. 

Decomposed  schist  and  quartz,  carrying  free  gold. 
Altered  country  rock,  carrying  free  gold. 


Actinolite-biotite  schist,  carrying  gold  and  silver. 
Do. 


Quartz  and  country  rock,  carrying  gold  and  silver. 
Quartz  and  country  rock,  carrying  free  gold. 
Quartz  and  schists,  carrying  free  gold. 


94  PRECIOUS  METALS. 

CUSTER  COUNTY. 


Minfc.  Country  rock  and  remarks. 


C'OJ-E   11ISTRICT. 


Ore  and  gangue. 


I):ivicl  Citv  Lightning Mica-schist,  with  much  quartz  on  foot  wall.    Strike.  X.  and  S. ;     Quartz  and  schist,  carrying  free  gold. 

dip,  83°  W. ;  ore  belt  8  feet.  wide. 


Knolwrott Mica-schist ;  dip,  N. ;  ore  belt  30  feet  wide  . 


rl'STKK    DI8T1UCT. 


Lenticular  masses  of  smoky  quartz,  carrying  free  gold. 


'  Hanging  wall  mica-schist ;  foot  wall  quart/He.    Strike,  N.  o°  W. ;     Quartz,  carrving  free  gold. 
dip,  GO«  W. 


( Iratul  Junction 


Hartford. 


Mammoth 


"Mica-schist.  Strike,  N.  5°  "W. ;  dip,  45^  W. ;  ore  belt  70  feet  wide. 

Mica-schist,  sometimes  garnetiferous.    Strike.  N.  5°  W. ;  dip,  45° 
W.  i  ore  belt  100  feet  wide. 


Auriferous  quartz,  with   little!  silver,   in  a  schist  consisting  of 
rauiated  aggregations  of  miuute  libers  of  tiemolite. 

Quartz  and  amphiholitic  schists,  carrying  free  gold. 


Mica-schist.  Strike,  N.  5°  W. ;  dip,  45°  W. ;  ore  belt  100  feet  wide.    Quartz  and  schist,  carrying  free  gold  and  some  silver;  garnet 


occiirs  with  the,  quaitz. 
Juartz  and  country,  carry 

Old  Charley Probably  Archaean  schists ;  no  specimens.  Ore  belt  300  feet  wide .    Quartz  masses  in  tine-grained  gneiss,  carrying  free  gold. 


Old  Bill    - i  Hanging  wall  qnartzose  mica-schist,  with  garnet  and  pyritc;      Quartz  and  country,  carrying  gold  and  little  silver. 

foot  wall  quartzite,  with  micaceous  layers. 


GEOLOGICAL  SKETCH  OF  MONTANA. 

PHYSICAL  DKSCRIPTION. — The  territory  of  Montana,  lying  along  the  northern  boundary  of  the  United  States, 
extends  westward  from  the  line  of  Dakota,  at  the  junction  of  the  Yellowstone  and  Missouri  rivers,  theoretically  to 
the  extreme  crest  of  the  Eocky  mountains. 

The  eastern  half,  which  consists  of  the  valleys  of  the  Yellowstone  and  Missouri  rivers  and  their  immediate 
tributaries,  belongs  more  properly  to  the  plain  country  of  the  northern  Missouri  valley.  This  portion  of  the  territory 
is  largely  occupied  by  various  Indian  reservations,  and  its  mineral  wealth  has  been  but  little  explored. 

Of  the  mountainous  western  half,  the  northern  portion,  adjoining  the  British  boundaries,  is  also  but  little  known. 
From  the  southern  boundary  of  Montana,  near  the  heads  of  the  Yellowstone  and  the  Missouri  rivers,  the  Rocky 
mountains  assume  a  northwestern  trend.  The  little  chartographic  knowledge  obtained  of  this  region  is  derived  from 
the  records  of  the  Northwest  Boundary  survey  and  from  the  explorations  for  a  route  for  the  Pacific  railroad  made 
under  the  War  Department,  which  give  a  partial  knowledge  of  certain  lines,  between  which  are  broad  gaps  whose 
topography  is  comparatively  unknown.  The  Rocky  mountains,  which  in  Colorado  are  a  compact  series  of  chains 
having  a  general  north  and  south  trend,  end  abruptly  in  southern  Wyoming;  but  in  northwestern  Wyoming  they  are 
represented  by  the  Wind  River,  Shoshone,  and  Big  Horn  mountains,  which  take  a  general  northwesterly  direction. 
The  Wahsatch  system  in  Utah  has  also  a  north  and  south  trend,  and  is  separated  from  the  Rocky  Mountain  system 
by  the  basin  of  the  Colorado  river.  Through  eastern  Idaho  this  chain  also  loses  somewhat  of  its  continuity,  and  the 
Rocky  Mountain  system  in  Montana  is  apparently  formed  by  the  junction  of  these  two  systems  of  elevation.  In 
general,  the  mountain  regions  in  western  Montana  are  less  elevated  than  those  of  Colorado  and  Utah  and  abound 
in  broad  open  valleys,  so  that  in  spite  of  the  northern  latitude  the  climate  is  relatively  mild.  They  are  well  watered, 
the  hills  and  valleys  support  an  abundant  growth  of  timber  or  grass,  and  in  many  of  the  valleys  a  limited  amount 
of  agriculture  is  possible. 

GEOLOGY. — Of  the  geology  of  Montana  but  little  is  definitely  known,  the  work  of  the  government  geological 
surveys  not  yet  having  extended  so  far  north.  The  surface  of  the  eastern  half  of  the  territory  is  probably  largely 
covered  by  the  Tertiary  and  Cretaceous  formations  which  are  found  on  the  great  plains  of  the  south,  while  along 
the  large  streams  are  broad  alluvial  valleys,  which  extend  well  up  to  the  foot-hills  of  the  mountains  and  are 
admirably  adapted  for  agriculture. 

As  well  as  can  be  determined  from  the  scanty  material  at  hand,  the  geology  of  the  mountainous  districts  of 
western  Montana  is  more  nearly  allied  to  that  of  the  Wahsatch  range  than  to  that  of  the  Rocky  mountains  of  Colorado, 
Indeed,  the  Archaean  uplift  of  the  Front  range  of  Colorado  finds  its  northern  continuation  in  the  Black  hills  of 
Dakota  on  a  line  with  the  extreme  eastern  boundary  of  Montana.  It  has  already  been  observed  (a)  that  the 
Wahsateh  range  forms  the  geological  center  of  the  Cordillerau  system,  and  that  between  the  sedimentary  series 
developed  on  either  side  of  this  central  axis  there  is  a  great  and  characteristic  difference.  The  Palaeozoic  formations, 
which  in  Utah  and  Nevada  reach  an  aggregate  thickness  of  over  30,000  feet,  in  Colorado  have  an  average  of  only 
about  5,000  feet.  Over  the  Great  Basin  area  the  Triassic  and  Cretaceous  rocks  are  entirely  wanting,  and  those 
developed  on  the  eastern  slope  of  the  Rocky  mountains,  extending  in  the  Wyoming  basin  as  far  as  the  flanks  of  the 
Wahsatch,  are  entirely  different  from  corresponding  horizons  in  western  Nevada  and  California.  The  heavy 
limestones  of  the  lower  portion  of  the  Palaeozoic  system  are  found  to  thicken  as  one  follows  the  line  of  the  Wahsatch 
northward  through  eastern  Idaho.  From  the  older  sedimentary  beds  of  Montana,  as  far  as  known,  no  fossils  have 
yet  been  obtained  by  which  to  determine  definitely  the  age  of  any  particular  horizon;  but  the  character  ot 
specimens  of  limestone  and  argillaceous  rocks  received  renders  it  probable  that  those  developed  in  the  mining  regions 

a  See  Heporte  of  the  U.  S.  Geological  Exploration  of  the  Fortieth  Parallel. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  95 

of  Montana  belong  to  the  lower  portion  of  the  Palaeozoic  horizon,  the  more  so  as  they  rest  directly  on  granites  or 
Archaean  schists.  The  only  geological  data  available  are  furnished  by  specimens  collected  in  the  southern  central 
portion  of  the  western  half  of  the  territory,  viz,  from  Lewis  ;md  Clarke.  Deer  Lodge,  Jefferson,  Madison,  and  Beaver 
Head  counties.  Of  the  geology  of  the  regions  extending  north  from  here  to  the  British  line,  through  Missoula  and 
Choteau  counties,  but  little  information  is  available.  That  obtained  from  these  counties,  which  is  furni>hed 
simply  by  specimens  of  country  rock  brought  in  by  the  experts  who  examined  this  region,  is  too  meager  to  afford  any 
ideas  of  general  structure ;  but  there  would  seem  to  be  an  upheaval  of  Archaean  rocks,  exposing  gneissic  formations, 
on  a  north  and  south  line  through  the  center  of  this  region.  Along  this  line  is  also  a  considerable  development  of 
so-called  granite,  in  which  the  most  valuable  ore  deposits  occur.  A  very  large  portion  of  this  granite,  however, 
proves  to  be  a  diorite  of  somewhat  singular  character,  possessing  certain  marked  characteristics,  which  is  found 
from  Madison,  through  Deer  Lodge,  north  to  Lewis  and  Clarke  county,  and  it  seems  probable  that  it  is  an  eruptive 
body  of  Archaean  age,  distinct  from  the  true  Archaean  granite.  The  specimens  which  have  been  microscopically 
examined  were  obtained  from  near  the  Lexington  and  Alice  mines,  at  Butte  City,  and  the  Deer  Lodge  lode,  in  Deer 
Lodge  county;  also  from  Union  lode  No.  2  and  Schafer  Mill,  in  Lewis  and  Clarke  county.  It  is  a  crystalline  rock, 
containing  both  orthoclase  and  plagioclase  feldspars,  the  latter  being  predominant,  with  but  little  quartz;  also  a 
large  proportion  of  basic  minerals,  among  which  hornblende,  augite,  and  biotite  all  occur.  This  association  is  the 
more  remarkable,  since  it  seems  that  these  minerals  are  all  original,  and  the  hornblende  is  not,  as  would  appear  at 
first  glance,  simply  a  decomposition  product  of  augite.  Under  the  microscope  the  former  is  seen,  indeed,  to  form  in 
many  cases  the  periphery  of  the  augite  masses;  but  it  is  not  fibrous,  like  the  uralitic  products  of  hornblende 
decomposition,  but  clear  and  homogeneous.  Hornblende  also  occurs  in  distinct  individuals;  and,  moreover,  there 
are  distinct  iutergrowths  of  biotite  and  hornblende,  both  fresh  and  with  the  biotite  leaves  lying  parallel  to  the 
orthopinacoid  of  the  hornblende.  It  would  seem,  therefore,  that  at  a  certain  period  in  the  growth  of  the  rock  the 
forma'jiou  of  augite  may  have  ceaseJMnd  the  hornblende  have  formed  about  the  already  existing  augite  particles. 
The  augite  is  pale,  and  contains  mul^magnetite  in  small  grains.  The  biotite  changes  to  a  green  mineral,  which 
does  not  seem  identical  with  the  ordinary  chlorite,  and  this,  in  turn,  changes  into  epidote.  Most  of  the  biotite  is 
fresu,  and  titanite,  apatite,  and  magnetite  are  present.  The  type  described  is  that  from  the  Union  lode.  That  from 
Schafer  Mill  contains  more  quartz  than  orthoclase,  and  some  of  the  quartz  is  intergrown  with  orthoclase,  so  as  to 
make  a  distinct  graphic-granite  structure,  visible  only  under  the  microscope.  Both  augite  and  biotite  are  abundant, 
but  hornblende  is  relatively  rare.  The  country  rock  of  the  Lexington  mine,  at  Butte,  has  the  same  general  character 
as  that  of  the  type  rock.  Much  of  the  hornblende  is  twinned,  and  intergrowth  of  biotite  is  common.  The  rock  of 
the  Alice  mine,  at  Butte,  is  somewhat  coarser  grained  than  the  others,  and  contains  a  less  proportion  of  basic 
silicates,  augite  being  entirely  absent  from  the  section  examined.  Mica  and  hornblende  are  about  equal  in  quantity, 
and  the  hornblende  has  frequently  the  outlines  of  the  prism,  showing  that  it  can  hardly  come  from  the  decomposition 
of  augite.  The  rock  from  Deer  Lodge  lode,  McClellan's  Gulch  district,  Deer  Lodge  county,  is  somewhat  different 
from  all  of  the  above.  It  contains  much  more  quartz  and  orthoclase,  and  augite  is  wanting,  although  hornblende 
and  biotite  are  similarly  intergrown  as  in  the  type  rock.  It  also  contains  apatite,  a  little  magnetite,  and  a  few  pale 
crystals  of  zircon,  but  no  titanite.  A  more  detailed  study  of  this  interesting  rock  than  it  was  possible  to  make  by 
the  aid  of  the  few  specimens  collected  by  the  census  experts  would  be  necessary  in  order  to  definitely  determine 
its  character.  In  the  subjoined  tables  it  has  been  provisionally  called  "  diorite-granite ",  to  distinguish  it  from  the 
normal  type  of  granite  which  occurs  in  the  same  district,  but  whose  structural  relations  to  it  are  as  yet  unknown. 

Of  rocks  which  could  be  definitely  determined  as  belonging  to  the  Secondary  eruptive  series  but  few  specimens 
were  brought  in.  There  can,  however,  be  no  doubt  that  they  are  of  frequent  occurrence  in  the  territory,  and  it  seems 
probable  that  to  this  type  may  belong  the  so-called  granites  which  overlie  the  contact  deposits  in  limestone  of  the 
Bannack  district.  But  little  reliance  can,  unfortunately,  be  placed  on  the  nomenclature  given  by  miners  to  the 
rocks  they  find  associated  with  their  ores,  since  they,  too,  often  pride  themselves  on  having  distinctive  names  of 
their  own,  quite  independent  of  any  scientific  usage.  The  so-called  porphyries  reported  from  Montana  mines 
have  proved,  where  specimens  have  been  sent  in,  to  be  more  or  less  altered  granites  or  gneisses.  Of  Tertiary  eruptive 
rocks  such  great  flows  exist  in  Idaho  on  the  south  and  west,  and  also  in  the  Yellowstone  park,  that  it  is  probable 
many  may  occur  in  the  territory.  The  only  definitely  known  occurrence  is  the  rhyolite,  which  breaks  through  the 
diorite-granite  at  Butte  City. 

ORE  DEPOSITS. — The  ores  of  Montana  are  mostly  of  gold,  silver,  and  copper,  either  separately  or  in  combination 
with  two  or  nvore  of  these  metals.  Argentiferous  lead  ores  also  occur,  but  in  far  smaller  proportion  than  in  Colorado, 
and  are  seldom  free  from  other  base  metals.  These  ores  are  found  either  in  veins  in  the  crystalline  rocks  or  as  irregular 
deposits  in  sedimentary  rocks,  sometimes  crossing  the  strata,  but  generally  more  or  less  coincident  with  bedding- 
planes.  Of  the  deposits  in  crystalline  rocks  the  majority  of  the  best  known,  and  those  whose  bodies  are  strong  and 
well  defined,  are  of  the  class  of  metamorphic  veins,  i.  e.,  their  vein  material  is  a  portion  of  the  country  rock,  more  or 
less  altered  along  certain  planes,  in  which  silica,  calcite,  and  metallic  minerals  have  replaced  portions  or  all  of  the 
original  constituents.  In  these  deposits  there  is,  as  a  rnle.  no  definite  limit  or  wall,  or,  at  the  most,  on  one  side 


96  PRECIOUS  METALS. 

only ;  and  it  is  evident  that  there  was  no  pre-existeut  open  fissure,  as  is  theoretically  supposed  to  have  been  the 
antecedent,  condition  of  the  "true  fissure  vein".  It  may  also  be  said  that,  as  far  as  our  present  knowledge  goes, 
there  is  no  valid  reason  for  supposing  that  such  deposits  are  any  less  permanent  or  rich  than  those  which  may  show 
evidence  of  having  been  deposited  in  a  pre-existing  open  fissure. 

IQ  some  cases  gold-bearing  ores  seem  to  be  simply  impregnations  of  the  gneissic  country  rock  with  auriferous 
pyrites,  and  probably  occur  in  lenticular  interlaniinated  quartz  masses,  such  as  on  a  very  much  larger  scale 
constitute  the  so-called  gold  veins  of  the  Black  hills  of  Dakota.  Deposits  in  limestone  seem  to  be  here,  as 
elsewhere,  very  irregular  in  form,  but  tend  to  follow  bedding  or  contact  planes  and  cross-joints  which  have  yielded 
more  easy  access  to  metallic  solutions.  Owing  to  the  superior  thickness  of  the  Palaeozoic  formations  in  this  region 
the  vertical  range  of  the  deposits  is  probably  much  greater  than  in  Colorado. 

A  considerable  proportion  of  the  ores  are  auriferous  pyrites  and  quartz,  sufficiently  oxidized  to  mill  freely;  but 
the  greater  value  and  bulk  are  those  of  more  complex  composition,  which  require  to  be  smelted.  These  have 
two  characteristics  which  distinguish  them  from  the  ores  of  Colorado  :  first,  a  usual  presence  of  copper,  rather  than 
of  lead,  as  a  silver-carrier,  and  of  manganese,  instead  of  iron,  in  that  part  of  the  ore  which  goes  into  the  slags  in 
smelting.  Chalcocite,  or  copper  glance,  is  one  of  the  most  common  minerals,  and  oxide  of  manganese,  passing 
into  carbonate  below  the  water  level,  is  exceptionally  frequent.  No  data  are  at  hand  for  making  even  an 
approximately  complete  list  of  the  minerals  which  occur  in  the  territory. 

PLACER  DEPOSITS. — Until  within  a  comparatively  few  years  the  main  precious-metal  production  of  Montana 
has  been  derived  from  its  placer  deposits,  which  are  exceptionally  rich.  Estimates  place  their  total  yield  at  over 
$50,000,000,  but  it  is  impossible  to  say  how  close  an  approximation  to  the  truth  these  estimates  may  be,  since  the 
grounds  on  which  they  are  based  are  not  given,  and  the  determination  of  the  yield  of  placer  mines  is  the  most  difficult 
task  the  mineral  statistician  has  to  undertake.  The  first  deposits  were  discovered  in  1861  in  the  Pioneer  district, 
on  Gold  creek,  a  branch  of  Deer  Lodge  river,  in  the  county  of  the  same  na«£.  For  many  years  the  production  of 
the  placer  mines  was  very  large ;  and  a  great  many  are  worked  at  the  preUit  day,  although  their  production  has 
somewhat  fallen  off  by  the  working  out  of  the  exceptionally  rich  deposits.  Hydraulic  mining  is  carried  on  to  a, 
very  considerable  extent,  and  many  Chinese  miners  find  ample  remuneration  in  working  over  abandoned  gulch  mines. 
Owing  to  an  unfortunate  combination  of  circumstances  the  census  data  were  collected  very  late  in  the  season,  when 
the  placer  mines  were  mostly  "abandoned  for  the  winter;  and  the  data  iu  regard  to  these  deposits  are,  consequently, 
very  incomplete.  The  deposits  which  are  worked  seem  to  have  been  found  mostly  in  rather  open  valleys,  but 
comparatively  high  up  in  the  mountains,  and  consist  consequently  of  rather  coarse  gravel.  For  deposits  of  this 
character  they  are  exceptionally  thick,  varying  according  to  data  from  5  to  65  feet ;  and  in  many  cases  actual  bed-rock 
had  not  been  reached,  but  only  a  clayey  seam  or  false  bed-rock,  below  which  the  gravel  is  said  to  be  barren. 

From  many  of  the  deposits  fossil  shells  and  petrified  bones  and  tusks  are  said  to  have  been  obtained.  No 
specimens,  however,  have  been  sent  in.  It  seems  likely,  therefore,  that  these  deposits  are,  as  a  rule,  older  than 
the  ordinary  river  gravels,  and  may  date  back  to  the  flood  period  following  the  Glacial  epoch.  Placer  deposits  are 
known  to  be  worked  in  Beaver  Head,  Madison,  Gallatin,  Meagher,  Jefferson,  Deer  Lodge,  Lewis  and  Clarke,  and 
Mi.ssonla  counties,  the  most  productive  of  which  have  been  those  of  Alder  gulch,  a  branch  of  the  Stinking  Water, 
at  the  head  of  the  Jefferson  river,  in  Madison  county.  Next  to  these  are  those  of  Deer  Lodge  county,  the  most 
important  of  which  is  the  Pioneer  district,  and  several  in  the  neighborhood  of  Butte  City  which  are  tributary  to 
the  Deer  Lodge  river,  the  Henderson  district,  near  Flint  creek,  and  the  McClellan  Gulch  district,  at  the  head  m  the 
Big  Blaekfoot  river. 

In  Lewis  and  Clarke  county  the  Last  Chance  district,  near  Helena,  has  been  a  large  producer;  and  important 
deposits  have  been  worked  on  both  sides  of  the  Missouri  river,  both  in  this  and  in  Meagher  county,  as  also  on  the 
east  slope  of  the  Big  Belt  mountains  of  the  latter  county.  Placers  have  also  been  worked  in  Gallatiu  county  north 
of  the  National  park,  along  the  tributaries  of  the  Yellowstone  river.  In  Beaver  Head  county  the  placers  near 
Bannack  have  a  bed-rock  of  conglomerate  with  lime  cement,  containing  shells  and  large  bones,  which  must,  it  seems, 
have  as  early  an  origin  as  the  Glacial  epoch.  The  gold  is  coarse  shot  gold,  with  a  relatively  large  proportion  of 
nuggets  as  large  as  walnuts;  and  that  derived  from  the  Montana  placers,  in  general,  has  a  higher  average 
grade  of  fineness  than  that  of  other  territories. 

DEER  LODGE  COUNTY  (SILVER  BOW  COUNTY). 

The  most  important  mining  district  in  the  state  is  Summit  valley,  near  Butte  City,  which,  since  the  legislative 
action  of  February,  1881,  is  now  included  in  the  new  county  of  Silver  Bow.  The  ore  deposits  of  this  district  all 
occur  either  in  true  granite  or  in  the  diorite-granite  already  described.  The  majority  of  the  veins  from  which  data 
are  available  have  an  east  and  west  strike  and  dip  at  a  high  angle  to  the  south.  Besides  the  granite  country 
rock,  rhyolite  occurs,  which  forms  the  so-called  butte  from  which  the  town  derives  its  name,  ramifications  from 
which  body,  it  is  suspected,  may  be  found  iu  the  neighborhood  of  some  of  the  important  mines.  The  veins  belong 
certainly  to  the  type  of  metamorphic  veins,  i.  e.,  although  the  richer  part  of  the  ore  is  often  found  in  a  gaugue  of 
almost  exclusively  siliceous  material  and  with  a  fairly  defined  wall  on  one  side,  on  the  other  there  is  no  definite 


GEOLOGICAL  SKETCH  OF  THE  ROOKY  MOUNTAIN  DIVISION.          97 

limit,  but  the  country  rock  is  found  to  yield  pay  material  for  a  varying  distance  from  the  main  ore  body,' and  the 
limit  to  which  the  impregnation  has  extended  is,  consequently,  not  determined,  since  only  that  which  it  would  pay 
to  work  is  extracted.  The  most  important  mines  of  the  district  are  the  Alice,  Lexington,  Belle,  Gagnon,  and  North 
Star.  Ores  rich  in  copper  and  silver,  and  carrying  an  exceptionally  large  proportion  of  manganese  minerals,  a  ti- 
the prevailing  type. 

The  Flint  Creel^  district,  near  Phillipsburg,  to  the  northeast  of  Bntte  City,  has  silver-bearing  ores  carrying 
zinc,  copper,  and  lead  minerals  in  a  limestone  generally  white  and  crystalline.  In  the  case  of  the  Salmon  mine 
granite  is  reported  as  occurring  on  the  hanging  wall  of  the  vein,  but  as  no  specimens  were  returned  it  seems 
questionable  whether  it  may  not  be  a  crystalline  porphyry. 

In  the  McClellan  Gulch  district,  at  the  head  of  the  Big  Blackfoot  river,  auriferous  quartz  is  found  in  a  rock 
resembling  the  diorite-granite  of  Butte  City. 

LEWIS  AND  CLARKE  COUNTY. 

The  principal  mines  of  Lewis  and  Clarke  county  appear  to  be  near  Helena  at  its  southern  extremity  and  along 
the  heads  of  Silver  creek  a  short  distance  north.  At  Helena  they  are  mainly  gold-bearing  veins  in  granite.  In 
the  Silver  Creek  region  they  are  also  gold-bearing  ores,  containing  a  little  silver,  but  occur  in  slates  and  slaty 
limestones ;  and  although  standing  at  a  high  angle,  and  called  fissure  veins,  it  would  seem  that  in  some  cases  at 
least  they  are  more  probably  segregations  of  quartz  and  mineral  in  bodies  lying  parallel  with  the  formation. 

JEFFERSON  COUNTY. 

In  Jefferson  county  the  ores  carry  both  gold  and  silver  in  varying  proportions,  and  the  mines  occur  in  various 
districts  on  either  slope  of  the  mountains  lying  west  of  the  Missouri  river.  The  ores  are  comparatively  free  from 
base  metals,  and  occur  in  felsite-po^B^ry  and  other  undetermined  eruptive  rocks,  and  in  limestones  parallel  with 
the  stratification-planes. 

MADISON  COUNTY. 

In  the  northeast  portion  of  Madison  county,  near  the  Jefferson  river,  are  the  Silver  Star  districts,  whose  ores 
occur  mainly  in  gneiss,  and  are  gold-bearing,  with  a  slight  admixture  in  some  cases  of  lead  and  copper  ores.  The 
Broadway  mine  is  reported  to  be  a  bedded  deposit  at  the  contact  of  limestone  with  granite. 

In  the  Mineral  Hill  district,  at  the  head  of  Willow  creek,  north  of  Virginia  City,  galena  and  quartz,  carrying 
both  gold  and  silver,  are  found  in  gneiss;  and  in  the  Red  Bluff  and  Hot  Springs  region,  near  the  Madison  river,  are 
ores  of  galena  and  pyrite,  also  mainly  in  gneiss,  carrying  both  gold  and  silver. 

Bnooh  Library 
BEAVER  HEAD  COUNTY. 

In  Beaver  Head  county,  near  Bannack  City,  auriferous  pyrite  in  quartz,  sometimes  associated  with  galena,  is 
found  in  limestone,  with  a  hanging  wall  of  so-called  granite.  The  strike  of  this  formation  seems  to  be  uniformly  to 
the  northeast,  with  a  shallow  dip  of  from  15°  to  20°  to  the  south  and  southeast.  As  already  stated,  it  seems  probable 
that  the  so-called  granite  is  a  quartz-porphyry  or  diorite.  Slates  and  limestones  can  be  traced  northward  from 
Bannack,  through  Argenta,  to  Gleudale,  near  Big  Hole  river.  At  first  they  preserve  the  westerly  dip  observed 
near  Baunack,  which  gradually  steepens,  and  becomes  vertical  some  15  miles  north  of  Argenta.  The  formation 
from  here  to  Glendale  dips  to  the  eastward.  Along  Trapper  creek,  which  flows  into  the  Big  Hole  from  the  west, 
are  easterly-dipping  slates,  apparently  underlying  the  limestone  which  is  found  at  Glendale.  At  its  head  is  a 
cliff  about  1,000  feet  in  height  of  blue-gray  limestone  beds,  underlaid  by  black  bituminous  shale,  dipping  16°  to 
the  westward;  half-way  up  the  cliff  are  the  deposits  of  the  Hecla  Consolidated  mines,  which  are  masses  of 
argentiferous  galena,  zincblende,  copper,  and  iron  pyrite,  and  their  oxidation  products,  occurring  on  the  stratification - 
planes  of  the  limestone  at  different  horizons.  These  ores  are  smelted  to  a  lead  bullion  and  a  copper  matte  carrying 
silver.  Big  Hole  river,  some  8  or  10  miles  higher  up,  runs  through  a  canon  cut  in  gneiss,  and  at  Dewey's  flat,  above 
the  caHon,  abundant  gold-bearing  quartz  veins  in  gneiss  are  said  to  occur. 

VOL  13 7 


98 


PRECIOUS  METALS. 

DEEE  LODGE  COUNTY,  (a) 


Mine. 


SUMMIT  VALLEY  DISTBICT. 

Alice... 


Anaconda  — 
Anglo-Saxon. 


Anselmo. 
Belle... 


Clear  Grit 

Colusa 

Cora 

Gagnon 

High  Ore 

Late  Acquisition 

Lexington 

Morning  Star 

Mountain 

Kational 


Conntry  rock  and  vein. 


Diorite-granite,  rich    in    plagioclase,  with  some  augite.    Vein : 
strike,  NE. ;  dip,  65°  NW.;  35  feet  wide. 

Granite  (?).    Vein:  strike,  E.  and  W. ;  dip,  75°  ;  8  feet  wide 

Granite.    Vein:  dip,  47°  S. ;  2J  to  5  feet  wide  


Granite,  containing  pyrites.    Vein :  strike,  E.  and  W. ;  dip,  7°  S. ; 
2  to  5  feet  wide. 

Diorite-granite.    Vein  vertical ;  strike,  E.  and  W 


Ore  and  gangue. 


True  granite.     Vein  :  strike,  NW. ;  dip,  70°  SW. ;  width,  15  to  17 
feet  (2  feet  productive). 

Granite  (!).    No  specimens.    Vein :  strike,  NW. ;  dip,  70° ;  14  feet 
wide. 

Granite(?).    No  specimens.    Vein  vertical;  strike,  E.  find  W. ; 
26  feet  wide,  including  horse  of  porphjry. 

Granite.   No  specimens.  No  distinct  walls.  Vein:  strike,  E.;  dip, 
80°  S. ;  width,  150  feet  (8  feet  pay). 

Decomposed  granite.  Vein  :  strike,  E.  and  W.  •,  dip,  45°  S. ;  12  to 
16  feet  wide. 

Diorite-granite.    Vein  :   strike,  E.  and  "W". ;  dip,  75°  S. ;   5  feet 
wide. 

Diorite-granite.    Vein:   strike,  E.  and  W. ;  dip,  30°  S. ;   8    feet 
wide. 

Granite.    Vein  vertical ;  strike,  E.  and  W 


Nettie 

North  Star. 


Shakspeare  . 
Shoubar  


Silver  Bow  Mining  Company 
(13  mines  reported  in  one 
schedule). 

Springfield 

Starrest 

Stevens 

Volunteer 


Wabash. 


INDEPENDENCE  DISTBICT. 

Mountain  Boy 


Self-rising  . 


FIJNTi  CREEK  DISTRICT.    . 

Algonquin 

Salmon 

Speckled  Trout 


Hope 

Scratch  Awl. 


M'CLEILAK'S  GULCH   DISTRICT. 

Deer  Lodge 

McClellan's  Gulch  lode  . . . 


Granite.    No  specimen.    Vein:  strike,  N"W.  and  SE. ;  dip,  75°  S. ; 

8  feet  thick. 
Decomposed  granite.    Vein :  strike,  E.  and  W. ;  dip,  80°  S. ;  20  feet 

wide. 

Granite.    Vein :  strike,  E.  and  W. ;  dip,  70°  S. ;  5J  feet  wide 

No  specimens.  Called  granite-porphyry,  may  be  rhyolite.  Vein : 
strike,  E.  and  W. ;  dip,  vertical ;  50  feet  wide. 

Granite  (diorite?).  Vein:  dip,  90°;  20  to  40  wide  >  foot  wall  not 
found. 

"  Soft  granite."  No  specimens.  Vein:  strike,  E.  and  W. ;  dip, 
70°  S. ;  12  feet  wide. 

Granite  and  svenite  (?).  No  specimens.  Veins:  strike,  about  E. 
and  "W.  ;  dip,  from  45°  to  00°. 

" Hard  granite."  No  specimens.  Vein:  dip,  70°  S. ;  pay-streak, 
4  feet  wide  on  foot  wall. 

Hanging  wall  like  granite.  Foot  wall  diorite  (?).  Vein:  strike,  1 
dip,  36°  S. 

Altered  syenite  (diorite  i).  Vein :  strike,  E.  and  W. ;  dip,  60°  S. ; 
4  feet  wide. 

"  Soft  granite."  Veins  (2)  16  feet  apart ;  strike,  E.  and  W. ;  dip, 
45°  8. ;  one  3  feet,  the  other  8  to  15  feet  wide,  the  former  the 
richer. 

Granite.  No  specimens.  Vein:  strike,  E.  and  W. ;  dip,  "10°" 
(probably  80°)  N. ;  100  feet  wide ;  pay-streak  2  to  6  feet. 


Native  silver,  and    sulphide,  with    carbonate    of  manganese, 
quartz,  and  pyrite,  carrying  gold  and  silver.    Gangne:  altered 
country. 

Chloride  of  silver,  malachite,  azurite,  chalcocite.  Gangue:  sili- 
ceous, may  be  altered  porphyry. 

Cerussite,  carbonate  of  manganese,  and  sulphide  of  silver  in 
quartz;  yellow  stains  of  antimony;  carries  silver  and  little 
gold.  Gangue:  decomposed  granite. 

Native  silver ;  argentite,  galena,  pyrite  ;  traces  of  manganese, 
copper,  and  gold  in  quartz.  Gangue:  decomposed  granite. 

Massive  chalcopyrite,  with  pyrite,  bornite,  freibergite  (?),  and 
nativesilver.withbutlittleqnartz.  Gangne:  clay,  withrounded 
granite  pebbles. 

Cellular  quartz,  containing  sulphuret  of  silver;  little  gold. 

Chalcocite,  massive  and  impregnating  the  granite.  Gaugue  aud 
horse  material ;  decomposed  quartz-bearing  granular  rock. 

No  specimens.  "Copper,  lead,  a  little  zinc  and  silver,  and  an- 
timony." 

Chalcocite,  silver-bearing.      Gangue:  wainlyquartz.  with  pyiite. 
Chloride  of  silver  (?)  in  cellular  quartz  ;  little  gold. 

Pyrite  and  chalcocite  in  quartz  ;  galena  aud  chlorides  said  to 
occur ;  little  gold.  Gangue :  decomposed  country  rock. 

Galena  and  cerussite,  with  rhodonite ;  silver  and  gold  bearing. 


Anriferon 
altered 


ito ;  native  silver  and  sulphxrret  in  quartz.  Gangue : 

•P 
Copper,    nnpecimens. 

Chalcocite  and  pyrite,  carrying  silver. 


Granite.     Vein:  strike,  about  E.  and  W. ;  dip,  70°  S. ;  2  feet  wide. 


"Porphyry"  (1).    No  specimens.     Vein:   strike,  E.  and  W. ;  dip, 
vertical ;  3  to  7  feet  wide. 


Psilomelane  and  horn-silver. 

Chloride,  black  sulphuret,  and  native  silver.    No  specimens. 

Largely  chalcocite,  carrying  little  silver. 

"Black  manganese,"  carrying  silver  and  little  gold.  No  speci- 
mens. 

Ores  carrying  galena,  cerussite,  pyrite,  chalcopyrite,  and  sul- 
phurets.  No  specimens.  Veins  paid  to  be  inclosed  in  porphy- 
ry, probably  decomposed  granite  (diorite). 

"  Sulphurets  of  silver  and  iron."    No  specimens. 
Freibergite  and  pyrite,  with  manganese  mineral.' 

Cellular  quartz  stained  yellow,  carrying  gold  and  silver.  No 
mineral  visible. 

Massive  zincblende  and  freibergite,  said  to  contain  also  horn- 
silver  and  galena. 

Cellular  quartz  with  yellowish  green  coating,  said  to  contain 
gold  and  chloride  of  silver.  Gangue :  "a  crumbling  mass  of  quartz 
and  feldspar  stained  reddish  yellow,  probably  altered  country. 


Quartz,  impregnated  with  galena ;  pyrite,  rhodochrosite,  with 
native  silver  on  joint-planes.  Gangue:  decomposed  country 
rock. 

Black  oxide  of  manganese,  with  gold,  silver,  and  copper.  No 
specimens. 


White  granular  limestone  (dolomitic?)  near  granite.    Deposit:  '  Galena,  blende,  gray  copper,  etc.,  in  quartz.    Oxide  of  manga- 
strike,  N.  20°  E.  ;  dip.  45°  E.,  in  irregular  bodies'.  nese  and  pyrite  also  occur ;  silver  hearinsr. 


Quartz,  with  zincblende  and  copper  stains,  carrying  silver. 


Granite  (?)  hanging  wall.    No   specimen.    Limestone  foot  wall. 
Deposit:  strike,  N.  20  E. ;  dip,  45°  E. 

Gray  crystalline  limestone,  fine-grained  on  hanging  wall,  coarser-  j  Mainly  crystalline  ziucblende  and  argentiferous  galena ;  said  to 
grained  on  foot  wall.    Vein  :  strike,  NE. ;  dip,  80°  SE. :  2  feet  ''      carry  ruby  silver, 
wide. 

Fine-grained  yellowish  limestone  ;  ore  deposit  in  bedded  masses;  •  Quartz,  impregnated  with  black  sulphurets  of  silver  and  car- 
strike,  E.  and  W.  ;  dip.  32°  :  4  to  9  feet  thick.  bonate  of  copper. 

Lhncstonr,  white  :ind  crystalline,    on  the  north  wall;    thinly  ,  Stained  quartz,  with  oxides  of  manganese  and  copper,  carrying      I 
bedded  and  slaty  on  the  south  wall.  Vein :  strike,  E.  6°  S. ;  dip,  '      silver, 
vertical :  2  feet  wide. 


Diorite-granite.      Vein:    strike,  N.  20  E. ;    dip,  20°  'W. ;  1  to   2 


Iron-stained  quartz. 


feet  wide, 
Diorite-granite.    Vein  :  strike,  NE. ;  dip,  20°  S.  E !  Iron-stained  quartz. 


a  In  February,  1881,  a  portion  of  Deer  Lodge  county,  including  the  Summit  Valley  district,  was  set  off  into  a  separate  county,  called  Silver  Bow. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  99 

LEWIS  AND  CLARKE  COUNTY. 


Mine. 


Country  rock  and  vein. 


Ore  and  gaugne. 


SILVER  CREEK  DISTRICT. 

Albion 

Penobscot,      Snowdrift,      and 
Courage. 

Belmont -. 


STKMPLE  DIBTBICT. 

Hickey  and  Bluebird 

Mount  Pleasant 

Sandfnrd  

Whip-poor-will 

OTTAWA    DISTRICT. 

Dromlommond 

OWYUEE  D18THICT. 

Union  lode  No.  2... 


Dark  slate.  Vein :  strike,  E.  81°  N. ;  dip,  70°  N. ;  18  inches  to 
11  feet  thick. 

Tough  greenish  slate,  with  imperfect  bedding  j  small  quartz 
veins.  Vein :  strike,  E.  and  W. ;  dip,  70°  N. ;  4  to  18  feet  wide. 

Slate  at  surface.  No  specimens.  Normal  granito  in  depth. 
Vein:  strike,  E.  and  W. ;  dip,  S. ;  average  width,  6  feet,  with 
two  branches. 


Dark  compact  slate,  with  imperfect  bedding ;  ore  bodies ;  strike, 
E.  and  W.;  dip,  SOPS. 

Slaty  limestone.     Deposit :   strike,  E.  and  W. ;  dip,  80°  S. ;  width, 
5  feet. 

Same  character  as  Hickey  and  Bluebird,  of  which  it  is  a  con- 
tinuation. • 

Slaty  limestone.    Vein:  strike,  E.  and  W. ;  dip,  75°  N. ;  3  feet 
wide. 


Syenitic  granite,  with  a  little  quartz.    Vein :  strike,  E.  and  W. : 
dip,  70°  S. ;  60  feet  wide  (40  feet  long). 

Diorite-granite,  with  biotite,  hornblende,  and  angite.  Vein :  strike  t ; 
dip,  30°  X. ;  3  feet  wide. 


Quartz,  with  oxides  of  iron  and  manganese,  little  lead  and  cop- 
per, carrying  gold  and  little  silver. 

Quartz,  with  oxides  of  iron  and  manganese ;  stibnite  in  pockets : 
carries  gold  and  trace  of  silver. 

Quartz,  with  some  calcite,  carrying  gold  and  silver. 


Mixture  of  quartz  and  feldspar,  carrying  gold  ;  gangue  of  flue, 
compact  limestone  in  center  of  ore  body  in  depth. 

Ore  deposit  like  the  former. 

Iron-stained  quartz. 

Mixture  of  qnartz  and  feldspar,  stained  with  aznrite  and  iron  oxide. 

White  gold-bearing  qnartz. 


JEFFERSON  COUNTY. 


CATARACT  DISTRICT. 

Boulder  •- 


Mantle 

CEDAR  FLATJfB  DISTRICT. 

Keating 

ELKRORN  DISTRICT. 

Alta 

A.  M.  Holter    . 


MOUNTAIN  DISTRICT. 
Little  Giant 

DISTRICT  SOT  OROAK1ZBD. 

Bonanza  Chief .'. . 

SILVER  STAB  DISTRICT. 

Aurora  Borealis 

Broadway .%-. 

Grasshopper  and  Cricket 

Grubstake 


Decomposed  porphyry.  Vein :  strike,  N.  70  W. ;  dip,  85°  HE. ; 
7J  feet  wide. 

Syenite  (t)  containing  a  little  qnartz.  Vein :  strike,  ENE. ;  dip, 
vertical ;  4  feet  wide. 

White  homogeneous  felsite,  impregnated  with  pyrites.  Vein : 
strike,  N.  and  S. ;  dip,  85°  W. ;  3?eet  wide. 

Compact  feleitic  porphyry.  Vein :  strike,  NE. ;  dip,  60°  NW.  j  8 
to  10  feet  wide. 

Limestone,  thin  bedded  and  compact  on  hanging  wall ;  granular, 
resembling  a  sandstone  on  foot  wall ;  ore  Dody,  dip  45°  to  the 
north  with  the  stratification. 


Greenish  eruptive  rock ;  undeterminable.    Vein :  strike,  E.  and 
W. ;  dip,  80°  S.;  4  to  6  feet  wide. 

No  specimen.     "Quartzose  rock,"   "bedded  mass  in  granite." 
Dip,  20°  NE. 

Fine-grained  gneiss.    Vein:  strike,  E.  andW. ;  dip,  45°  S.;  2 feet 
wide. 

Hanging  wall  dark  impure  limestone;  foot  wall  granite.    De- 
posit: strike,  NW.  and  SE. ;  dip,  38°  S. ;  thickness,  15  feet. 

Syenite(f),  probably  gneiss.    No  specimen.    Vein:  strike,  E.  and 
W. ;  dip,  50°  S. ;  5  to  6  inches  wide. 

Even-grained  gneiss.    Vein:  strike,  NW.j  dip,  45°  NE. ;  2  feet 
wide. 


Iron-stained  quartz,  carrying  gold. 
Gold-bearing  qnartz,  with  pyrito ;  little  silver. 

Massive  pyrite,  carrying  gold  and  silver. 

Qnartz,  carrying  galena  and  pyrite,  silver,  and  a  little  gold. 
Qnartz,  with  argentiferous  galena,  some  native  and  horn-silver. 

Iron-stained  mass,  qnartz  and  clay  carrying  gold. 

Iron-stained  siliceous  matter,  containing  gold  and  traces  of  silver. 


Gold-bearing  qnartz  with  galena;  little  carbonate  of  copper  and 
iron  oxide. 

Yellow  ferruginous  jasper,  with  spots  of  hematite,  chalcedony, 
and  calcite  in  the  fissures ;  carries  gold. 

Iron-stained  gold-bearing  quartz. 

Decomposed  yellow  rock,  probably  gneiss  carrying  silver. 


MADISON  COUNTY. 


HOT   BPRDIQS    AXD    RED    BLUFF 
DISTRICTS. 


Boaz 

Cordwainer. 
Red  Bluff... 


Red  Chief 

MIKKBAL  HILL  DISTRICT. 

White  Pine... 


Gneiss.    Vein :  strike,  NW. ;  dip,  45°  E.  s  2  feet  wide . 


Fine-grained  biotite-gneiss.    Vein :  strike,  NW.  j  dip,  50°  NE. ; 

2J  feet  wide. 
Gneiss.    Vein :  strike,  E.  and  W. ;  dip,  41°  N. ;  3  to  6  feet  wide. . . 


Granite  (f).    No  specimens.    Vein :  dip,  48°  NE. ;  4  feet  wide. . . 


Gneiss,  with  rhombic  pyroxene.    Vein :  strike,  E.  and  W. ;  dip, 
45°  S. ;  18  inches  wide. 


Crumbling,  stratified  rock,  iron-stained,  and  carrying  gold.  Al- 
tered country. 

Crumbling,  iron-stained  gneiss,  carrying  gold  ;  little  copper. 

At  surface  red  or  blue  jasper,  with  some  pyrito  and  galena, 
carrying  gold  and  silver.  Below  water  level  solid  mass  of 
pyrite  and  galena,  with  little  qnartz. 

Iron-stained  qnartz,  carrying  gold  and  silver. 


Massive  qnartz,  with  some  galena,  carrying  gold  and  silver. 


100 


PRECIOUS  METALS. 

BEAVER  HEAD  COUNTY. 


Mine. 


Country  rock  and  vein. 


Ore  and  gangue. 


BAXXACK  DI8TBICT. 

Dakota  and  Blue  Grass . . . 


Excelsior 

French  

Golden  Leaf . 
Springfield  .. 
Washington  . 


JiALD  MOUNTAIN  DISTRICT. 

Elkhorn  .. 


TBAFFBK  DISTRICT. 


Hecla 

Keokuk  .. 


Hanging  wall  granite ;  foot  wall  limestone.    No  specimens.  De- 
posit: strike,  NE. ;  dip,  15°  SE. ;  8  feet  thick. 

Hanging  wall  granite   (?)   and  trap;    foot  wall  limestone.     No 
specimens.    Deposit:  strike,  NW. ;  dip,  20°  SE.  ;  81'oet  thick. 

Hanging  wall  granite  (?) ;   foot  wall  limestone.     No  specimens. 
Deposit:  strike,  E.  and  W.;  dip,  15°  S. ;  15  to  40  feet  thick. 

Same  as  French.    Deposit :  10  to  80  feet ;  dip,  15°  S. ;  strike,  NE. 
and  SW. ;  10  to  50  feet  thick. 

Hanging  wall  granite  (?) ;  foot  wall  limestone.    No  specimens. 
Strike,  NE. ;  dip,  15°  S. ;  5  feet,  thick. 

Like  the  preceding. 


Granite.    No  specimens.    Vein  :  strike,  NE.  and  SW. ;  dip,  88°  N. 


Dolomite,  blue  and  gray.    Ore  deposit  follows  the  stratification- 
planes.    Strike,  N. ;  dip,  10°  W. ;  2J  feettbick.    Several  bodies. 

Limestone,  siliceous  on  hanging  wall,  crystalline  on  foot  wall. 
Ore  deposit  following  the  stratification-planes.    Dip,  35°  SW. 


Quartz,  pyrite,  and  siliceous  oxide  of  iron,  carrying  gold. 
Iron-stained  quartz  and  pyrite. 
Siliceous  iron,  with  pyrite,  carrying  gold. 
Oxide  of  iron,  free  gold,  argentiferous  galena. 
Auriferous  iron-stained  quartz. 


"Zincbleude,   black  copper,  gray  copper,  chloride,  and  native 
silver."    No  specimens. 


Contains  galena, cernssite,calamine,andcopperininerals.  Gangue: 
white  crystalline  limestone. 

Oxides,  carbonates,  and  sniphnrets  of  silver,  lead,  and  copper. 
No  specimens. 


GEOLOGICAL  SKETCH  OF  NEW  MEXJCO, 

The  territory  of  New  Mexico,  adjoining  Colorado  on  the  south,  has  a  somewhat  larger  area,  and  is  included 
between  the  one  hundred  and  third  degree  of  longitude  west  of  Greenwich  and  the  thirty-second  west  of  Washington, 
and  extends  from  the  thirty-seventh  degree  of  north  latitude  to  the  boundary  of  Mexico,  which,  except  in  the 
southwestern  corner,  is  formed  by  the  thirty-second  degree  of  north  latitude.  Its  climate  is  even  drier  thau  that 
of  Colorado,  which  may  be  due  to  the  fa*jt  that  it  has  no  concentrated  high  mountain  mass  to  act  as  a  condenser  to 
the  moisture-laden  winds  coming  from  the  southwest.  The  mountain  systems  of  Colorado  end  abruptly  near  its 
northern  border,  the  Colorado  range  continuing  with  a  gradually  decreasing  elevation  as  far  south  as  Santa  Fe, 
while  the  San  Juan  mountains,  to  the  west  of  San  Luis  park,  siuk  beneath  the  Cretaceous  plains  almost  before  the 
boundary  is  reached.  Its  surface  is  made  up  of  an  irregular  series  of  detached  mountain  cbains,  stretching  across 
the  middle  of  the  territory  iu  a  southwesterly  direction,  with  a  mesa  country,  belonging  to  the  Colorado  plateau 
region  on  the  northwest,  and  broad  arid  plains,  a  continuation  of  those  in  northern  Texas,  stretching  to  the  eastward. 
Across  the  middle  of  this  area  from  north  to  south  runs  the  Bio  Graude  river,  whose  valley  presents  many  analogies 
with  that  of  the  famous  Nile  valley  of  Egypt.  Its  climate  is  warm  and  equable,  and  its  alluvial  soil,  which  occupies 
a  comparatively  narrow  strip  on  either  side  of  the  river,  in  general  not  more  than  2  miles  in  width,  is  of  exceptional 
fertility.  Like  the  Nile,  it  is  subject  to  periodical  overflows,  and  the  area  of  its  arable  land  can  probably  be 
increased  by  a  more  perfect  system  of  irrigation  than  has  beeu  carried  on  by  the  Mexican  population  which  at 
present  occupies  it.  With-  the  exception  of  this  valley,  there  is  little,  if  any,  land  in  the  territory  which  can  be 
considered  available  for  agriculture,  not  from  any  want  of  fertility  of  soil,  but  from  the  absence  of  water  for 
irrigating  purposes.  The  main  wealth  of  the  territory  lies,  therefore,  in  its  grazing  lands  andi*s  mineral  resources. 

Our  geographical  knowledge  of  this  area  is  as  yet  extremely  imperfect,  being  derived  only  from  the  meander 
lines  made  in  early  years  by  various  government  expeditions  iu  exploring  routes  for  a  Pacific  railroad  and  from 
detached  maps  of  portions  of  the  central  and  northern  regions  made  by  the  explorations  west  of  :hc  100th  meridian 
under  Lieutenant  Wheeler. 

In  regard  to  its  geology  our  information  is  equally  fragmentary,  being  derived  from  the  notes  made  by 
Professors  Jules  Marcou  and  J.  S.  Newberry,  who  accompanied  the  earlier  railroad  explorations,  and  of  Messrs.  G. 
K.  Gilbert,  E.  E.  Howell,  and  Professor  J.  J.  Stevenson,  who  accompanied  different  parties  of  the  Wheeler 
exploration.  The  census  material  with  regard  to  this  territory  is  also  exceptionally  incomplete,  owing  to  the  fact 
that  Colonel  Charles  Potter,  to  whom  was  intrusted  the  duty  of  visiting  and  reporting  on  its  variqus  mining 
districts,  was  treacherously  waylaid  and  killed  by  a  party  of  seven  Mexican  robbers  while  in  the  discharge  of  this 
duty,  and  while  his  work,  though  nearly  completed  in  the  field,  still  needed  his  personal  supervision  to  put  it  into 
an  intelligible  form. 

GENERAL  GEOLOGY. — The  Archaean  island  which  stretched  through  the  state  of  Colorado  from  its  northern  to 
its  southern  boundary  ended  abruptly  in  New  Mexico,  its  continuation  to  the  southward  being  marked  only  by  a 
series  of  more  or  less  submerged  reefs  in  the  ocean,  which  covered  this. area  until  the  close  of  the  Cretaceous  period. 
Up  to  this  time,  therefore,  the  waters  of  the  ocean  had  free  access  to  the  Colorado  plateau  region,  and  at  the  present: 
day  the  coal-bearing  or  Cretaceous  rocks  are  known  to  extend  over  a  great  portion  of  the  territory.  Owing  to 
the  limited  rainfall,  the  valleys  and  mountain  slopes  are  much  more  heavily  covered  by  Quaternary  debris  than  those 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION.  101 

of  Colorado,  and  the  character  of  the  underlying  rocks  is  therefore  more  difficult  to  recognize.  The  Cretaceous 
formations  are,  however,  known  to  extend  from  the  plain  country  westward  to  the  Rio  Grande  valley,  and  in  the 
northwestern  portion  of  the  territory  to  connect  with  the  Colorado  plateau  region,  while  they  still  form  the  surface 
rock  over  a  very  considerable  area.  In  the  latter  region  they  are  known  to  extend  beyond  its  western  boundaries, 
but  in  the  mountain  region,  in  the  southwestern  portion  of  the  territory,  they  have  either  been  entirely  eroded  off,  or 
else,  owing  to  some  dynamic  movement  later  than  the  Palaeozoic  period,  as  yet  unproved,  they  were  not  deposited- 
Of  eruptive  rocks  there  is  considerable  development  of  quartz-porphyries  and  other  Secondary  rocks,  especially  in 
the  southwestern  portion  of  the  territory ;  but  no  sufficient  study  has  been  made  of  them  to  determine  definitely 
their  age  or  relation  to  the  Palaeozoic  beds  in  connection  with  which  they  are  found.  The  only  known  Tertiary  beds 
are  those  near  San  Ildefonso,  which  are  supposed  to  be  of  Pliocene  age.  As  yet,  therefore,  there  is  no  record 
to  determine  the  period  at  which  the  Tertiary  eruptive  rocks,  which  are  so  largely  developed  in  the  territory, 
were  first  poured  out  on  the  surface.  Of  these,  as  Mr.  Gilbert  shows,  an  immense  crescent-shaped  area  extends 
through  eastern  Arizona  and  western  New  Mexico  to  the  volcanic  group  of  the  San  Francisco  mountain  at  its 
northwestern  point,  and  to  that  of  Mount  Taylor,  in  New  Mexico,  at  its  northeastern.  They  also  cover  considerable 
isolated  areas  to  the  east  of  the  Rio  Grande.  That  eruptive  activity  has  continued  until  comparatively  recent 
times  is  proved  by  the  existence  of  numerous  actual  jcraters  and  cinder-cones  in  a  region  35  to  40  miles  southwest 
of  Mount  Taylor,  from  which  streams  of  lava  flowed  out  in  every  direction,  extending  at  least  50  inile»  to  the 
westward  and  to  an  unknown  distance  to  the  eastward.  These  recent  lava  flows  are,  according  to  Mr.  Gilbert, 
all  basaltic,  while  the  mass  of  Mount  Taylor  consists  of  an  older  eruptive  rock,  described  by  him  as  something 
between  a  basalt  and  trachyte,  and  which,  from  analogy  with  other  regions,  may  be  supposed  to  be  eitherandesiteor 
a  still  earlier  porphyrite.  Professor  Stevenson  also  describes  extinct  craters  as  existing  to  the  east  of  Santa  Fe  near 
the  Turkey  mountains  and  flows  of  basaltic  lavas  filling  the  canon  of  the  Mora  river.  The  northwestern  part  of 
the  territory,  therefore,  which,  from  the  Naciiniento  range  westward,  belongs  to  the  mesa  region,  and  south  of  the 
Carboniferous  anticlinal  of  the  Zuui  range  consists  a  broad  belt  of  lava  extending  to  the  plains  of  San  Augustin,  is 
covered  by  rocks  of  too  recent  age  to  afford  much  promise  to  the  prospector.  It  is  in  the  mountain  groups 
stretching  across  the  territory  to  the  southeast  of  this  region  that  the  principal  developments  have  thus  far  been 
made.  Among  these  Mr.  Gilbert  distinguishes  two  prevailing  trends — a  northwesterly  and  a  north-aud-south 
direction.  The  former,  which  is  more  common  in  the  south  western  portion  of  the  territory,  he  considers  as  belonging 
to  a  portion  of  the  Basin  range  system,  which  stretches  through  Arizona  in  the  direction  of  the  Sierra  Nevada; 
the  latter  he  connects  with  the  Colorado  system.  In  these  different  regions  the  rocks  thus  far  recognized  are 
either  Archaean  or  Palaeozoic.  Granite  and  gneiss  are  often  found  as  a  nucleus,  and  here,  as  elsewhere,  are  distinctly 
unconformable  with  the  later  beds  of  the  Palaeozoic  formations,  which  consist  of  quai  tzites,  sandstones,  limestones, 
and  shales.  Fossil  evidence  has  been  found  of  the  existence  of  the  Cincinnati  group  of  the  Silurian,  the  Waverly 
or  sub-Carboniferous,  and  the  characteristic  Carboniferous  limestones  of  the  Rocky  Mountain  region.  Of  Mesozoic 
formations  the  Trias  is  recognized  in  the  northern  portion,  and  is  described  by  Professor  Stevenson  as  being  extremely 
thin  or  at  times  entirely  wanting  along  the  edge  of  the  mountains  northeast  of  San  ta  F6.  The  aggregate  thickness 
of  the  Cretaceous  rocks,  which  consist  as  elsewhere,  of  sandstones  and  shales,  is  given  by  Professor  Stevenson  at 
2,000  feet.  Mr.  Gilbert  states  that  coal  is  found  throughout  this  entire  formation,  but  only  that  of  the  middle 
is  of  economic  importance.  Professor  Stevenson,  on  the  other  hand,  makes  the  Galisteo  beds,  which  have  been 
practically  developed  in  the  northeastern  part  of  the  territory,  belong  to  the  Laramie  group,  or  extreme  upper  member 
of  the  Cretaceous.  Of  the  age  of  the  coal-beds  which  have  recently  been  developed  in  the  neighborhood  of  the  Rio 
Grande  valley  in  the  central  and  southern  portion  of  the  territory  no  information  is  available.  In  the  succeeding 
description  will  be  given  the  few  facts  it  has  been  possible  to  obtain  with  regard  to  the  geology  of  the  mining 
regions  thus  far  developed,  following  as  far  as  possible  the  division  by  counties. 

COLFAX  COUNTY. 

The  western  portion  of  Colfax  county  includes  the  southern  end  of  the  Rocky  mountains,  locally  called  the 
Taos  and  Baldy  ranges,  which  consist  of  a  nucleus  of  Archaean,  overlaid  by  Carboniferous  limestone  and  flanked 
by  Mesozoic  beds.  Throughout  the  region  there  is  a  considerable  development  of  eruptive  rocks  classed  as  trachy  tic, 
and  on  the  adjoining  plains,  on  either  side,  are  recent  flows  of  basalt.  Partially  included  in  the  range  is  the 
longitudinal  Moreno  valley,  whose  Quaternary  deposits  are  said  to  constitute  rich  gold  placers.  Besides  the  placers, 
gold  veins  are  said  to  have  been  developed,  but  no  working  mines  are  reported.  Specimens  of  gray  copper  ore, 
associated  with  coal,  have  been  brought  in  from  points  along  the  eastern  foot-hills  of  the  mountains.  Their  geological 
position  is  not  known  The  matrix  is  a  sandstone  resembling  those  of  the  Cretaceous  formation,  and  it  may  be, 
that  they  occur  in  connection  with  the  singular  longitudinal  dike  mapped  by  Professor  Stc-vensou.  Galena  and 
considerable  placer  deposits  occur  in  Taos  county,  adjoining  Colfax  on  the  west. 


102  PRECIOUS  METALS. 

SANTA  Ffi  COUNTY. 

The  oldest  mines  of  the  territory,  said  to  have  been  worked  by  the  Spaniards  when  they  first  came  here,  over 
three  centuries  ago,  are  probably  in  Santa  Fe"  county. 

The  Los  Cerillos  district  embraces  the  Los  Gerillos  mountains  north  of  the  Galisteo  river,  and  the  Ortiz  mountains 
to  the  south.  In  the  former  an  eruptive  rock,  probably  rhyolite  or  trachyte,  breaks  through  the  Cretaceous  strata. 
In  this  are  found  irregular,  thin  deposits  of  galena  and  the  celebrated  turquoise  mines,  which  have  been  worked 
for  years  both  by  Mexicans  and  Indians.  This  mineral  occurs  apparently  as  an  impregnation  along  the  cleavage 
faces  of  the  country  rock.  Along  the  Ortiz  mountains  and  the  Placer  mountains  to  the  south  are  valuable  placer 
deposits,  which  in  places  have  been  penetrated  60  feet  without  reaching  bed-rock.  But  little  is  known  of  their  extent 
or  character,  and,  owing  to  the  want  of  water,  they  have  thus  far  been  but  little  developed.  The  Placer  mountains 
consist  of  Archaean  rocks  overlaid  by  Carboniferous  limestone.  Veins  of  auriferous  pyrites  are  said  to  occur  in  the 
Archaean ;  also  magnetic  iron  ore.  In  the  limestones  are  deposits  following  the  stratification  and  occurring  in 
connection  with  what  is  called  porphyry,  which  contain  both  auriferous  pyrites  and  sulphurets  of  copper,  more 
or  less  oxidized,  carrying  silver. 

In  Bernalillo  county  the  Sandia  mountains,  which  rise  abruptly  to  the  east  of  Eio  Grande  valley,  are  formed, 
according  to  Marcou,  of  Carboniferous  strata  dipping  to  the  eastward,  and  have  been  apparently  lifted  to  their 
preseut  position  by  a  fault.  On  their  slopes  occur  also  rich  placer  deposits.  West  of  the  Eio  Grande  copper  has 
been  obtained  from  the  sandstones  of  the  Trias  in  the  neighborhood  of  Abiquiu.  The  ores  are  found  as  carbonates 
and  oxides,  replacing  fossil  plants. 

SOCOKRO  COUNTY. 

In  the  Socorro  mountains,  lying  opposite  the  town  of  Socorro,  on  the  Eio  Grande  river,  according  to 
Professor  B.  Silliman,  (a)  are  several  large  veins  of  heavy  spar  running  in  a  northeast  and  southwest  direction  and 
dipping  40°  to  the  northwest,  carrying  chloride  of  silver  and  vanadium-bearing  mimetite.  The  Magdalena 
mountains,  30  miles  west  of  this,  consist,  according  to  the  same  authority,  of  slates,  limestones,  and  quartzites,  resting 
on  gneiss  and  traversed  by  porphyritic  eruptions.  The  Juniata  lode  is  described  as  a  vertical  deposit  of  lead 
carbonates  between  porphyry  and  slates  reaching  a  maximum  thickness  of  65  feet,  but  of  low  grade  in  silver.  Galena 
and  ziucbleude,  with  calamine  and  anglesite,  are  also  found  in  the  same  deposit. 

In  the  Oscuro  mountains,  to  tbe  east  of  the  Eio  Grande,  are  deposits  of  copper  glance,  azurite,  and  malachite, 
carrying  a  little  silver  and  gold  in  a  siliceous  conglomerate.  These  ores,  like  those  already  mentioned,  are  associated 
with  remains  of  fossil  wood  and  various  plants,  and  are  said  to  carry  from  10  to  60  per  cent,  of  copper.  This 
conglomerate,  because  of  the  resemblance  of  the  deposits  to  those  of  Eussia,  which  occur  at  this  horizon,  is  regarded 
as  of  Permian  age  by  Professor  Silliman.  The  reason  for  such  determination  seems  rather  inadequate,  in  view  of  the 
fact  that  the  Permian  group  has  not  yet  been  definitely  recognized  in  the  Eocky  mountain  system,  to  which  these 
deposits  belong,  and  that  the  beds  in  which  similar  deposits  have  been  found  in  Colorado  and  New  Mexico  have 
hitherto  been  determined  as  Triassic. 

The  Negretta  or  Black  range  extends  across  Socorro  county  into  Grant  county,  adjoining,  and  is  apparently 
connected  with  the  Miembres  range.  It  is  so  called  because  of  the  dark-colored  firs  which  cover  it.  According 
to  Professor  Silliman,  this  range  is  intersected  by  powerful  lodes  carrying  gold,  silver,  copper,  zinc,  and  lead,  but  no 
indication  is  given  with  regard  to  the  character  of  the  country  rock,  except  that  porphyry  is  mentioned  as  inclosing 
one  vein.  In  the  western  portion  of  the  county,  at  the  head  of  the  San  Francisco  river,  is  the  Mogollon  district,  in 
which  islands  of  Archaean  granite,  with  Palaeozoic  rocks  resting  on  them,  occur  on  the  southern  border  of  the  lava 
area  already  mentioned ;  and  in  the  limestones  of  the  latter  are  rick  deposits  of  copper,  in  some  cases  carrying 
both  gold  and  silver.  No  returns  from  individual  mines  are  at  hand. 

LINCOLN  COUNTY. 

.  In  Lincoln  county,  to  the  east  of  Socorro  county,  about  125  miles  from  the  Eio  Grande  valley,  is  the  White 
Oaks  district,  in  a  mountain  group  generally  known  as  the  Sierra  Blanca.  Gold  ores  are  reported  as  discovered  in 
this  district,  but  no  reliable  data  are  at  hand  as  regards  either  their  value  or  the  geology  of  the  district. 

DONA  ANA  COUNTY. 

In  the  Organ  mountains,  to  the  east  of  the  Eio  Grande,  15  miles  from  Las  Cruces,  argentiferous  galena  ores  are 
reported.  Near  Hillsboro',  on  the  west  of  the  Eio  Grande^  are  placer  deposits,  and  gold  veins  are  said  to  have 
been  discovered. 

The  most  important  mining  district  of  the  county  is  Lake  valley,  which  is  on  the  eastern  slope  of  the 
Miembres  mountains.  This  range,  according  to  Mr.  Gilbert,  has  a  core  of  Palaeozoic  limestone,  with  lava  on  the 
western  slope.  The  ore  bodies  occur  following  the  bedding-planes  of  limestone  beds,  which  dip  to  the  eastward. 
The  foot  wall  is  a  heavy-bedded  bluish-gray  limestone,  above  which  are  thinly-bedded  shaly  limestones,  carrying 

a  Trans.  A.  I.  M.  E.,  Feb.,  1882. 


GEOLOGICAL  SKETCH  OF  THE  ROCKY  MOUNTAIN  DIVISION. 


103 


fossils  of  the  Waverly  group.  The  ore  consists  of  argentiferous  galena  and  cerussite,  with  chlorides  and 
chloro-broinides  of  silver  in  a  gangue  of  red  and  brown  hematite,  with  some  oxide  of  manganese,  and  silica  in  the 
form  of  chert.  Professor  Silliman  reports  also  the  occurrence  of  ranadinite.  The  deposits  apparently  resemble  in 
their  manner  of  occurrence  those  of  Leadville.  Irregular  masses  and  dikes  of  eruptive  rocks  are  reported  also  as 
occurring  in  the  region,  but  their  lithological  character  and  direct  relation  to  the  ore  deposits  is  not  yet  definitely 
known. 

GRANT  COUNTY. 

Grant  county  has  been  the  principal  mineral  producer  of  the  territory,  its  most  important  mines  being  located 
within  an  area  of  which  Silver  City  and  Fort  Bayard  form  the  center.  In  the  Miembres  district,  on  the  west  slope 
of  the  Miembres  mountains,  to  the  east  of  Silver  City,  are  argentiferous  lead  ores  in  limestones  of  Paleozoic 
age.  The  limestones  are  fossiliferous,  and  dip  to  the  eastward ;  but  it  is  not  known  whether  they  correspond  to 
those  of  Lake  valley  on  the  east  or  to  those  in  the  neighborhood  of  Silver  City  on  the  west.  The  deposits  follow 
the  bedding,  having  a  foot  wall  of  limestone,  with  shale  on  the  hanging  wall.  To  the  north  of  Silver  City  is  the 
Pinos  Altos  mountain,  which  consists,  according  to  Mr.  Gilbert,  of  granite,  with  porphyry  overlapping  on  one 
side  and  the  lavas  of  the  Diablo  range  on  the  other.  The  veins  are  quartz  veins,  carrying  both  gold  and 
silver,  having  a  general  north  and  south  strike,  and  standing  at  a  steep  angle.  According  to  the  census 
specimens,  they  occur  in  both  diabase  and  quartz-porphyry.  At  Lone  mountain,  to  the  south  of  Silver  City,  are 
ferruginous  deposits,  carrying  chlorides  and  sulphides  of  silver,  following  the  bedding  of  limestones,  which  dip  to 
the  northeast. 

The  Burro  mountains  to  the  west  of  Silver  City  consist,  according  to  Howells,  of  two  bodies  of  Archaean  granite, 
the  one  covered  by  heavily-bedded  trachytes,  the  other  by  Palaeozoic  beds  dipping  to  the  northeast.  In  the  latter 
occur  argentiferous  lead  ores,  with  chlorides  and  sulphurets  of  silver.  Those  in  the  Chloride  Flat  district  occur 
between  limestone  beds,  and  those  in  the  Silver  Flat  district  between  an  overlying  quartz-porphyry  or  diorite  and  an 
underlying  limestone  or  dolomite.  From  the  silver-bearing  limestones  Mr.  Howells  obtained  characteristic  fossils 
of  the  Cincinnati  group. 

In  the  Santa  Kita  mountains,  according  to  Mr.  Gilbert,  argentiferous  galena  occurs  in  Carboniferous  limestone, 
and  veins  carrying  gold  and  copper  in  porphyry.  The  famous  Santa  Rita  mines  are  near  the  crest  of  the  range  at 
the  contact  of  the  Carboniferous  limestone  and  an  overlying  porphyry.  The  Shakspeare  or  Virginia  district  is 
about  25  miles  southwest  of  the  Burro  mountains,  in  the  Pyramid  range,  which  is  made  up,  according  to  Mr.  Gilbert, 
of  "basalt  and  trachyte,  overlying  an  older  lava,  in  which  occur  the  quartz  veins.  The  most  prominent  of  these  stand 
up  above  the  weathered  surface  of  the  rock,  while  others  less  prominent  carry  argentiferous  galena  ores  with 
chloride  and  native  silver.  The  country  rock  most  probably  belongs  to  the  older  or  Secondary  type  of  eruptives, 
although  Mr.  Gilbert  describes  it  as  resembling  the  propylite  of  v.  Eichthofen. 

SANTA  Ffi  COUNTY. 


Mine. 


Country  rock  »nd  vein. 


Ore  and  gangne. 


L08  CEBRILLOB  DISTRICT. 

Marshall  Bonanza 

8ILVXB  BUTTE  DI8TBICT. 

San  Pedro  and  Canon  del  Agua 


Supposed  to  be  rhyolite. 
wide. 


Vein  vertical;  strike,  N.  38°  E. ;  2 feet 


Quartzite  and  porphyry  on  banging  wall ;  limestone  on  foot  wall, 
No  specimens.    Deposit  v  •  a  the  formation.    Strike,  K.  and  S. ; 


dip,  15°  E. ;  30  feet  thick. 


!  Argentiferous  galena  and  cerussite,  with  black  oxide  of  manga- 
nese and  minute  crystals  of  wulfenite  (?). 

Iron-stained  quartz,  with  pyrite,  carrying  gold ;  7  to  8  feet  thick  on 
vail;  underlaid  by  deposit  of  azurite,  malachite,  cbryso- 


hangingwa    ,  , 

colla,  cuprite,  chalcopyrite,  and  bournonite. 


No  specimens. 


.     GRANT  COUNTY. 


CHLOBIDK  FLAT  DISTRICT. 

Bremen 


Limestone ;  light-gray  and  crystalline  on  ban 
and  nne-grauied  on  foot  wall.  Strike.  N.  3° 
posit  in  irregular  bodies  on  foot  wall. 


ring  wall,  dark-blue 
ET;  dip,  13°  E.    De- 


Providence  

LONE  MOUNTAIS  DISTRICT. 

Cosette 


Dark -blue  limetone  or  dolomite. 
85°  E. ;  average  width,  2  feet. 


M1EMBBE8  DISTRICT. 

Commercial 


McGregor . . . 
Naiad  Queen 


.  Dark  carbonaceous  shale; 
specimens.    Deposit  in 
dip,  SE. 

Da  ik  carbonaceous  ahale  ; 
specimens.  Deposit  in 
dip.  SE. 

•  Dark  carbonaceous  shale  : 
specimens.  Deposit  in 
dip,  SE. 


Vein :  strike,  N.  40°  W. ;  dip, 


.  I  Dolomitic  limestone;  light  brown,  crystalline,  and  called  porphyry, 
on  banging  wall;  reddish  with  conchoidal  fracture  .on  foot 
wall.  Deposits  with  the  bedding.  Strike,  NW.  ;  dip,  21°  E., 
in  irregular  bodies. 


;  foot  wall,  fossiliferous  limestone.   Xo 
irret'ular  Dockets  with  the  beddini;  : 

foot  wall,  fossiliferuus  limestone.    Xo 
irregnlar  pockets  with  the  bedding  ; 

foot  wall,  fossil  iforons  limestone.    Xo 
irregular  packets  with  the  bedding  ; 


Cerargvrite,  argentite,  and  galena.    Gangue :  barite,  flnorite,  and 
argillaceous  slate. 

Iron-stained  quartz  and  limestone,  carrying  chlorides  and  sulphu- 
rets of  silver. 


Siliceous  hematite,   carrying   chloride  and  sulphide  of  silver. 
Gangue:  altered  foot  wall. 


Argentiferous.    Xu  specimens. 


Chlorides  and  sulphurets  of  silver,  with  cernssite  and  carbonate 
of  iron  in  altered  limestone. 

Chloridesandsulphnretsof  silver  and  carbonates  (?)  of  iron;  tree 
milling. 


104 


PRECIOUS  METALS. 

GRANT  COUNTY— Contiuued. 


Mino. 


FINOS   ALTOS   DISTRICT. 

Langston 

Mina  G  raudo 

Ohio 

Pacific  No.  2 

SILVER  FLAT  DISTRICT. 

Massachusetts  and  New  Mex- 
ico. 


Sherman. 


Country  rock  and  vein. 


Much  altered  diabase,  called  limestone.    Vein:  strike,  N.  15°  E. ; 
dip,  70°  SK 

Called  quart/loss  granite,  or  trachyte.    No  specimens.    Vein: 
strike,  N.  and  S. ;  dip,  80°  E. ;  2  lent  wide. 

Decomposed  quartz-porphyry.    Veia:  strike,  N.  and  S. ;  dip,  E. ; 
4  I'eet  wide. 

Probably  diabase.  Vein:  strike,  N.  and  S. ;  dip,  75°  E.;  2  feet  wide 


Hanging  wall  light-colored  quartz-porphyry ;  foot  wall  dark 
dolomite.  Deposit  with  the  bedding.  Strike,  N.  32°  W. ;  dip, 
85°  E. ;  up  to  15  feet  thick. 

Hanging  wall  altered,  eruptive  rock,  possibly  dinette;  foot  wall 
dark-Drown  dolomite.  Deposit  with  the  bedding.  Strike,  N. 
and  S.  j  dip,  15°  E. 


Ore  and  gangue. 


Ganguo  corussito,   chlorides,   and  sulphides  of  silver  carrying 
gold. 

Aurifernns  quartz,  with  chlorides  and  snlphidcs  of  silver.    Xo 
specimens. 

Galena,  chalcopyrite,  with  barite  in  quartz,  carrying  gold  and 
silver. 

Mixture  of  barite,  quartz,  pyrite,  and  galena,  carrying  gold  and 
silver. 


Chlorides  and  sulphides  of  silver,  with  quartz  and  calcite. 


Galena,  with  chloride  and  sulphide  of  silver. 


286  PRECIOUS  METALS. 


CHAPTER  VI.— LEAD  SMELTING  AT  LEADVILLE,  COLORADO. 

BY  S.  F.  EMMONS. 


PLANT. 

INTRODUCTORY. — Although  a  very  large  amount  of  technical  data  on  the  various  smelting  works  of  the  West 
was  collected  by  the  census  experts,  they  were  not  found  sufficiently  complete  to  serve  as  the  sole  basis  for  a 
detailed  description  of  the  processes  employed ;  nor  do  these  works  in  general,  as  far  as  they  are  open  to  public 
inspection,  present  any  features  which  are  unusual  or  new  to  metallurgical  science.  At  Leadville,  however,  where 
the  numerous  smelting  establishments  produce  annually  about  $15,000,000  worth  of  argentiferous  lead  bullion, 
metallurgists  have  necessarily  acquired  an  unusual  amount  of  practical  experience  in  the  conduct  of  the  operations 
of  lead  smelting  and  in  the  management  of  the  business  connected  therewith.  It  has  therefore  been  judged 
expedient  to  present  a  succinct  account  of  the  natural  and  economical  conditions  of  smelting  at  this  point,  of  the 
character  of  the  plant,  and  of  the  processes  employed.  For  this  purpose  recourse  has  been  had  to  the  MS.  of  a 
report  by  Mr.  A.  Guyard  on  the  lead  smelting  of  Leadville,  which  is  to  appear  as  an  appendix  to  a  monograph 
on  the  geology  and  mining  industry  of  that  district.  An  abstract  of  this  report  has  been  made  by  Mr.  W.  F. 
Hillebrand,  and  is  supplemented  by  data  obtained  from  census  material  and  by  himself  and  the  writer  personally, 
which  appears  in  the  following  pages.  In  this  the  chemical  investigations  and  calculations  made  by  Mr.  Guyard 
have  been  freely  used,  and  the  two  illustrations  which  accQmpany  it  are  taken  from  his  plates;  but  all  discussion 
as  to  the  fitness  or  unfitness  of  methods  employed,  or  of  theoretical  questions  arising  therefrom,  has  been  avoided. 

TOPOGRAPHICAL  CONDITIONS. — An  important  condition  in  the  disposition  of  smelting  works,  as  well  as  of 
quartz-mills  and  other  reduction  works,  is  that  the  force  of  gravity  may  be  used  as  an  aid  in  handling  the  material 
to  be  treated,  which  is  generally  of  a  heavy  and  bulky  nature.  To  such  a  disposition  the  surface  character  of  the 
Leadville  region  is  admirably  suited  by  nature.  The  town  itself  is  situated  on  a  gently  sloping  mesa  included 
between  Evans  gulch  on  the  north  and  California  gulch  on  the  south,  at  the  western  base  of  the  foot-hills  of  the 
Mosquito  range,  in  which  its  ores  occur.  Along  the  high  banks,  which  rise  from  the  bottom  of  either  of  these 
gulches  to  the  comparatively  flat  surface  of  the  mesa,  and  at  a  sufficient  elevation  to  allow  room  for  the  slag  dumps 
below  them,  are  located  the  various  smelting  works.  They  are  thus  situated  so  that  from  the  mines  an  equally 
favorable  grade  leads  either  to  the  upper  or  the  lower  portion  of  the  works,  and  the  railroad  which  follows  the 
surface  of  the  mesa  sends  its  branches  on  the  level  of  or  above  the  charging  floor,  and  thus  delivers  its  freight  of 
fuel  or  of  ore  where  it  may  descend  through  the  various  stages  of  the  process  until  the  final  product,  the  bars 
of  bullion,  is  obtained. 

DISPOSITION  OF  THE  PLANT. — No  less  than  sixteen  smelting  works  have  been  built  at  Leadville  in  the  few 
years  that  have  elapsed  since  its  mines  were  opened.  Of  these,  however,  a  number  have  been  closed,  some 
temporarily,  others  permanently.  The  general  plan  in  these  works  is  that  adopted  elsewhere,  and  involves  the 
occupation  of  two  principal  floors.  The  lower  of  these  floors  is  at  such  a  height  above  the  adjoining  valley 
bottom  as  to  afford  a  convenient  opportunity  for  dumping  slag  and  other  waste.  On  this  floor  the  furnaces  are 
built,  and  room  is  also  commonly  provided  for  the  blower  and  the  engine  by  which  it  is  actuated.  The  furnaces 
are  usually  placed  in  a  row  within  a  single  iuclosure,  but  sometimes  they  have  a  wall  intervening  between  them. 
The  upper  floor  is  on  a  level  with  the  feeding-door  of  the  furnaces,  from  12  to  14  feet  above  the  lower,  and  affords 
space  for  ore-bins,  fluxes,  mixing-beds,  and  the  operations  connected  with  charging  the  furnaces,  such  as  crushing 
and  sampling.  When  the  slope  of  the  ground  is  great,  however,  the  storage  bins  for  ore  and  fuel  are  sometimes 
placed  at  a  still  higher  level,  with  passages  for  wagons  between.  One  roof  generally  covers  the  whole  establishment, 
with  the  exception  of  the  offices,  laboratory,  and  scales,  which  commonly  occupy  detached  buildings. 

FURNACES. — Shaft  furnaces  only  are  employed  in  Leadville.  Of  these  two  varieties  were  in  use  during  the 
census  year,  the  one  presenting  a  circular  horizontal  cross-section,  sometimes  called  the  Piltz  furnace,  while  the 
other  is  rectangular;  but  in  1882  the  latter  had  entirely  replaced  the  former.  While  the  circular  section  presents 
advantages  in  the  regularity  of  the  descent  of  the  charges,  it  is  more  expensive  in  construction,  and  the  diameter 
of  the  hearth  is  limited  by  the  strength  of  the  blast;  indeed,  with  any  ordinary  blowing-engine  a  round  furnace  can 
be  successfully  worked  only  when  it  is  of  very  moderate  dimensions.  The  rectangular  or  Easchette  furnace,  on  the 
other  hand,  may  be  constructed  with  a  width  at  the  tuyeres  corresponding  to  the  strength  of  the  blast-engines,  and 
the  production  may  be  increased  by  increasing  the  length  of  the  cross-section.  The  horizontal  elongation  of  the 
furnace  has  its  limits,  indeed,  as  has  been  proved  by  the  history  of  the  rectangular  Raschette  furnaces  in  Europe, 
but  the  capacity  may  nevertheless  be  increased  considerably  above  that  of  a  circular  furnace  of  similar  construction 
without  deleterious  effects  upon  the  working.  In  lead  smelting,  and  especially  in  smelting  argentiferous  lead  ores, 


Department  of  the  Interior. 


Plate  I. 


Tenth  Census  of  the  United  States. 


.y.    3.     SECTIOH 


Cast  Iron  Wron^l  fron 


Fin>  Brick 


Scald:!  inch,  to  6  iect 


j.J.     SEOTIOU   QFET. 


Fif.    2.     SECT IOH 


JI  BTBTI  3=1. 


RECTANGULAR  FURNACE 


4 

LEAD  SMELTING  AT  LEADVILLE,  COLORADO.  287 

it  is  very  undesirable  to  employ  the  high  pressure  blasts  required  by  a  circular  furnace  of  large  diameter,  since  the 
higher  temperatures  which  result  promote  the  production  of  fumes  which  are  only  imperfectly  recovered  and  are 
always  difficult  of  treatment. 

The  rectangular  and  the  round  furnaces  of  Leadville  are  constructed  on  the  same  general  plan  so  far  as  height, 
method  of  support,  water-jackets,  tuyeres,  etc.,  are  concerned,  but  the  sizes  adopted  vary  greatly,  the  limits  of 
capacity  being  from  15  to  40  tons  in  twenty-four  hours. 

Plate  I,  Fig.  1,  represents  a  rectangular  furnace  in  elevation  drawn  to  a  scale  of  G  feet  to  the  inch,  and  Fig.  2 
the  same  furnace  in  horizontal  section  at  the  tuyere  level.  Fig.  3  shows  a  vertical  section  of  the  same  furnace  on  its 
longer  diameter,  and  Fig.  4  a  horizontal  section  at  the  charging-doors.  The  masonry  shaft  ( C)  rests  upon  a  cast-iron 
plate  (0),  supported  by  pillars  (P),  in  order  that  there  may  be  no  unnecessary  weight  on  the  lower  portion  of  the 
furnace.  The  walls  for  some  distance  above  and  below  the  tuyeres  are  formed  of  sectional  water-jackets  (B), 
constructed  of  cast  or  wrought  iron  or  of  steel.  In  the  furnace  illustrated  the  water-jackets  are  twelve  in  number, 
firmly  bolted  together  and  provided  with  openings  for  the  insertion  of  the  tuyeres  (N).  A  cold  water  pipe  (M) 
runs  around  the  furnace  above  the  water-jackets,  and  water  is  admitted  to  each  of  them  by  a  faucet  (Y).  Outlets 
(M'}  for  the  hot  water  and  gutters  (T)  for  its  removal  are  also  shown  in  the  illustrations.  The  interval  (b)  between 
the  water-jackets  and  the  plate  on  which  the  shaft  of  the  furnace  rests  is  filled  with  fire-brick,  which  can  be  readily 
removed  in  case  of  necessity.  The  lower  ends  of  the  water-jacket  rest  upon  the  hearth  (X).  This  consists  of  cast- 
iron  plates  (a)  bolted  together  and  lined  with  a  thick  coating  of  fire-brick  or  of  "steep"  (brasque),  a  mixture  of  fire- 
clay and  coke-dust,  either  in  equal  parts,  or  in  the  proportion  of  two  of  the  former  to  one  of  the  latter.  The  usual 
form  of  the  hearth  is  shown  in  the  illustrations;  this,  however,  is  modified  in  detail,  according  to  the  working  of  th« 
furnace  and  the  judgment  of  the  manager  or  smelter,  changes  in  it  involving  no  modification  of  the  iron  plates. 

The  hearth  plates  include  also  the  lead  well  L  and  the  so-called  "siphon  tap".  A  similar  device  was  long  ago 
applied  to  the  small  charcoal-iron  blast-furnaces  of  Silesia,  to  permit  of  the  manufacture  of  castings  without 
tapping  the  furnaces;  it  was  not  successful,  however,  the  iron  chilling  too  rapidly  for  the  object  in  view,  owing  to 
its  high  melting  point.  This  arrangement  was  introduced  into  lead  smelting  in  Eureka,  Nevada,  by  Mr.  Albert 
Arents  with  great  success,  and  has  since  been  widely  adopted  both  in  this  country  and  abroad.  The  lead  rises 
through  the  oblique  tap-hole  JJ  shown  in  Fig.  1  to  the  same  level  in  the  well  which  it  occupied  in  the  furnace,  and  can 
be  baled  into  the  molds  at  leisure,  and  without  the  disturbance  of  the  furnace-working  incident  to  the  old  method 
of  tapping  at  long  intervals. 

At  the  end  of  the  furnace  just  above  the  hearth  an  opening  ( V)  is  left  in  the  water-jacket  to  facilitate  the  tapping 
of  slag.  This  opening  is  filled  with  clay,  in  which  a  hole  can  be  pierced  when  required,  allowing  the  slag  to  pass 
through  an  inclined  gutter  ( U),  shown  in  the  illustrations,  into  a  slag-buggy.  A  hood  ( W)  is  generally  placed  over  th* 
tapping-hole  to  draw  off  the  fumes  emitted  during  the  tapping.  The  number  of  tuyeres  varies  with  the  size  of 
the  furnace,  depending  mainly  on  the  length  of  the  cross-section.  A  tuyere  is  always  placed  at  the  end  of  th« 
furnace  opposite  the  slag-tap,  and  sometimes  also  above  it ;  this  last,  however,  is  somewhat  in  the  way,  and  is 
often  omitted.  A  sliding  valve  (/)  at  the  elbow  of  the  nozzle  admits  of  the  inspection  of  the  interior  of  the  furnace. 
The  tuyeres  are  connected  with  the  main  blast-pipe  (I)  by  canvas  hose  (K),  the  flexibility  of  which  permits  their 
withdrawal  from  the  furnace  when  necessary.  This  convenient  device  is,  of  course,  applicable  only  when  cold  air 
is  supplied  to  the  furnace,  as  is  almost  invariably  the  case  in  lead  smelting.  Feed-openings  (II)  on  the  upper  floor  ar« 
closed  by  sliding  doors  (8).  The  furnace  terminates  upward  in  a  short  chimney  (E)  and  may,  in  case  of  need,  be  run 
without  the  dust-chambers,  with  which  it  is  connected  by  a  flue  (F )  indicated  in  the  illustration. 

As  an  example  of  recent  construction,  the  furnaces  in  the  works  of  Eddy,  Jajnes  &  Grant,  at  Denver,  may  be 
cited.  There  are  eight  of  these  furnaces  of  the  same  pattern,  all  built  in  the  spring  of  1882.  The  height  to  the 
charying-door  is  18  feet;  the  dimensions  3  feet  below  the  charging-door  are  60  by  102  inches;  at  the  top  of  the 
jackets,  48  by  92i  inches,  and  at  the  tuyere  level,  36  by  80J  inches.  Each  furnace  has  ten  tuyeres,  four  on  each 
side  and  one  at  each  end.  The  capacity  of  each  is  about  30  tons.  The  waste  gases  and  fumes  are  drawn  from  all 
these  furnaces  at  a  point  below  the  charging-doors  into  large  dust-chambers  connecting  with  a  single  stack — a  very 
convenient  arrangement  so  far  as  the  comfort  of  the  workmen  is  concerned;  whether  it  is  accompanied  by  any  ill 
•effect  upon  the  working  of  the  ore  is  regarded  as  uncertain,  but  each  furnace  is  provided  with  an  independent  stack, 
to  be  used  in  the  event  of  its  proving  desirable  to  return  to  the  ordinary  practice. 

Plate  II  shows  a  furnace  with  a  circular  horizontal  section  on  the  same  scale  as  the  rectangulargf'urnace 
illustrated  on  Plate  1,  and  a  comparison  will  show  that  the  general  principles  governing  the  construction  are  the 
same  in  both.  A  main  point  of  difference  is  in  the  anchoring,  which  in  the  square  furnace  is  necessarily  effected 
by  bars  (<^),  while  the  same  object  is  more  conveniently  attained,  when  the  section  is  circular,  by  a  shell  of  sheet 
iron  (J)  composed  of  plates  about  a  quarter  of  an  inch  in  thickness.  The  diameter  of  round  furnaces  at  the  tuyere 
level  is  from  33  to  48  inches,  and  the  capacity  varies  with  this  dimension. 

DUST-CHAMBERS. — The  appliances  for  catching  flue-dust  in  the  Leadville  smelting  works  are  generally  very 
imperfect,  butthe  reproach  does  not  apply  to  Leadville  alone,  for,  however  extensive  the  system  employed  elsewhere, 
it  fails  to  accomplish  its  purpose  completely.  It  is  said  that  some  English  lead  works  have  dust-chambers  no  less 
than  5  miles  in  length,  and  yet  fail  to  recover  all  the  dust  carried  from  the  furnaces ;  some  of  the  Leadville  works, 
however,  make  no  attempt  to  collect  the  flue-dust,  a  practice  unworthy  of  imitation.  The  ordinary  provision 


288  PRECIOUS  METALS. 

consists  of  brick  chambers  on  or  below  the  charging-floor,  either  divided  into  sections  by  walls  and  curtains  or 
not.  One  such  chamber  is  75  feet  long,  25  feet  wide,  and  15  feet  in  height,  and  another  of  the  same  length  is  only 
•i  feet  wide  and  6  feet  high.  The  dust-chambers  are  sometimes  built  of  iron  instead  of  brick,  and  the  circuitous 
direction  given  to  the  current  by  the  interposition  of  walls  and  curtains  in  brick  chambers  is  then  often  obtained  by 
the  use  of  adjoining  vertical  cylinders,  the  air  and  fumes  entering  the  bottom  of  one  and  the  top  of  the  next. 

BLAST-ENGINES. — The  blowing  engines  employed  are  most  commonly  of  the  Baker  rotary  pattern,  though  at 
one  establishment  the  Root  blower  is  in  use.  The  pressure  of  the  blast  furnished  by  these  blowers  varies  from 
half  an  inch  to  1^  inches  of  mercury,  or  say  from  one-fourth  to  three-fourths  of  a  pound  per  square  inch,  the  most 
usual  tension  being  1  inch  of  mercury,  or  about  half  a  pound  per  square  inch.  Where  several  blowers  are  employed 
in  furnishing  blasts  to  more  than  one  furnace  the  pressure  is  equalized,  and  the  probability  of  an  interference  with 
the  work  through  the  stoppage  of  a  blower  is  decreased  by  connecting  them  all  with  the  same  main  blast-pipe. 

The  iron  work  of  the  furnaces  is  sometimes  made  by  Denver  firms,  but  usually  the  entire  plant  is  ordered 
from  the  East. 

BARTLETT  FILTEK. — An  experiment  was  made  at  one  of  the  works  with  this  arrangement  for  collecting 
flue-dust  which  gave  some  interesting  results.  The  following  is  condensed  from  Mr.  Guyard's  description : 

The  stack  of  one  of  the  square  furnaces  was  connected  with  a  Sturtevant  fan  by  means  of  a  sheet-iron  flue, 
through  which  the  fumes  were  drawn  from  the  furnace  and  blown  through  a  sheet-iron  pipe  150  feet  in  length, 
which  was  connected,  by  means  of  two  branch  pipes,  with  two  boxes  of  thin  sheet  iron.  The  dust  was  collected  in 
the  sheet-iron  pipe  as  in  an  ordinary  flue.  Each  branch  pipe  was  provided  with  a  damper,  or  valve,  similar  to  those 
used  in  stovepipes,  so  that  the  fumes  could  be  distributed  to  one  or  both  of  the  boxes  at  pleasure.  Each  box 
consisted  of  a  dust-chamber  and  a  fireplace,  the  former  being  provided  with  sliding  doors,  placed  at  either  extremity, 
and  the  fireplace  with  doors  in  front  and  sheet  iron  pipes  at  the  back,  communicating  with  a  stack.  At  the  top  of 
each  of  the  dust-chambers  were  twenty-eight  apertures,  to  each  of  which  was  fastened  a  cloth  bag,  30  feet  high, 
suspended  to  the  beams  of  a  light  wooden  structure,  in  which  the  apparatus  was  inclosed,  and  which  was  provided 
with  very  large  openings  for  ventilation.  When  the  apparatus  is  at  work  the  fumes  blown  iu  distribute  themselves 
in  the  dust-chambers  and  ascend  the  cloth  bags,  through  which  they  are  filtered.  The  gases  come  out  perfectly 
colorless  and  free  from  any  lead  dust  or  even  soot.  The  wind  entering  freely  through  the  apertures  of  the  building 
shakes  the  bags,  and  the  dust  with  which  they  are  charged  falls  back  into  the  dust-chambers.  When  a  sufficient 
quantity  of  this  dust  has  been  accumulated,  the  doors  connecting  with  the  fireplace  are  opened  and  a  light 
wood  fire  is  kindled.  The  soot  soon  catches  fire  and  burns  off,  leaving  the  dust  white.  During  a  run  of  five  days 
3,030  pounds  of  calcined  dust  were  caught  in  a  Bartlett  filter  from  one  furnace.  The  experiment  was  not  entirely 
satisfactory,  owing  to  defects  in  the  manner  in  which  it  was  carried  out;  but  the  defect  was  one  of  arrangement, 
and  by  no  means  inherent  in  the  filter.  The  furnace  was  worked  without  closing  the  feed-hole,  as  with  an  ordinary 
dust-chamber.  The  Sturtevant  fan  consequently  drew  in  as  much  air  as  smoke,  so  that  the  chamber  of  the  furnace 
had  to  be  left  half  open,  and  about  half  the  smoke  escaped  directly  into  the  open  air.  The  use  of  this  arrangement 
was  abandoned  by  the  owners  of  the  works  partly  on  account  of  the  expense  involved  and  partly,  as  stated  by 
them,  on  account  of  the  large  percentage  of  arsenic  (15  to  20  per  cent.)  in  the  condensed  matter  and  its  low  tenor 
in  silver.  As  Mr.  Guyard,  in  his  analysis  of  this  substance,  found  extremely  little  arsenic  and  much  lead,  chiefly 
combined  with  phosphoric  acid,  chlorine,  and  bromine,  it  is  difficult  to  imagine  on  what  ground  the  presence  of 
arsenic  iu  such  quantity  could  be  inferred.  Mr.  Guyard's  analysis  is  supported  by  the  fact  that  arsenic  is  present 
to  but  small  extent  throughout  the  district,  while  phosphoric  acid  exists  in  large  quantities  in  many  of  the  ores. 

EAW  MATERIAL. 

ORES. — The  ores  of  Leadville  are  remarkably  pure  argentiferous  lead  ores.  They  are  locally  divided  into  two 
general  classes:  the  "sand  carbonates",  which  are  loose,  sandy  masses  of  carbonate  of  lead  with  chloride  of  silver, 
and  the  "hard  carbonates",  which  are  masses  of  porous  siliceous  material  with  a  varying  proportion  of  hydrated 
oxides  of  iron  and  manganese,  carrying  carbonates  of  lead  and  chlorides  of  silver,  and  sometimes  containing  a 
considerable  proportion  of  unaltered  argentiferous  galena.  As  a  rule,  with  the  exception  of  mechanical  mixtures  of 
clay  and  varying  proportions  of  iron  and  silica,  they  contain  but  few  foreign  ingredients.  Intimately  associated 
with  the  carbonates  is  generally  a  little  pyromorphite  or  chloro-phosphate  of  lead,  amounting  in  one  exceptional 
case  to<0  and  in  another  to  30  per  cent,  of  the  whole.  Sulphate  of  lead  also  occurs  iu  small  quantity,  with  small 
and  variable  amounts  of  oxidized  compounds  of  copper,  arsenic,  antimony,  and  manganese.  The  latter  is  o/ten 
abundant,  and  is  associated  with  or  replaces  iron  oxide.  Ores  which  are  rich  in  manganese  are  generally  poor  in 
silver.  The  galena  is  frequently  covered  by  a  coating  of  carbonate  showing  clearly  the  alteration  of  the  sulphide, 
first  to  sulphate,  and  then  to  carbonate.  In  some  few  mines  bismuth  and  vanadium  ores  have  been  found.  But  a 
small  proportion  of  the  ores  smelted  is  furnished  by  districts  outside  of  Leadville.  Of  this  the  greater  part  comes 
from  Ten-Mile  district,  in  Summit  county,  and  especially  from  the  Eobinson  mine,  whose  deposits  carry  much  pyrite 
and  zincblende.  The  silver  in  the  oxidized  ores  is  present  in  combination  with  chlorine,  bromine,  and  iodine, 
either  as  chloride,  chloro-bromide,  or  chloro-bromo-iodide,  as  the  analyses  on  page  289  of  specimens  from  several 
mines  made  in  the  laboratory  of  the  United  States  geological  survey  at  Denver  show. 


Department  of  the  Interior. 


Plate  [I. 


Tenth  Census  of  the  United  States. 


iy    3      SECTION  OH  f  <S 


r 


Clay 


Scale,  i  inch  \o   e    feet   01    1.72 

TEE  I 


1IETEH3 

1  7 


Z.    EECTIOJI  ON  tt  p. 


CIRCULAR  FUKNACE 


LEAD  SMELTING  AT  LEADVILLE,  COLORADO. 


289 


. 

R.E.  Lee  mine. 

Amie  mine. 

Big  Pittsburgh 
mine. 

Chloride  of  silver  

21  589 

15  755 

99  9C5 

Bromide  of  silver  

77  986 

84  091 

Koike 

Iodide  of  silver  

0  425 

0  154 

0  035 

» 


Large  masses  of  chloride  of  silver,  or  horn-silver,  have  been  found,  and  on  several  occasions  tons  of  ore  have 
been  taken  from  the  R.  E.  Lee  mine  assaying  from  8,000  to  15,000  ounces  of  silver  to  the  ton  and  almost  entirely 
free  from  lead.  According  to  Mr.  Guyard,  sulphide  of  silver  is  sometimes  present  in  small  quantity. 

The  Leadville  ores  in  general  contain  little  or  no  gold,  its  presence  not  being  easily  detected  in  the  ore  itself, 
but  only  being  shown  in  the  final  product.  The  average  daily  output  of  the  mines  in  1880  is  placed  by  Mr.  Guyard  at 
from  700  to  800  tons,  and  the  total  smelting  capacity  of  the  furnaces  at  700  tons  per  diem. 

FLUXES. — The  fluxes  used  in  Leadville  are  limestone  and  hematite.  During  the  census  year  the  limestone 
used  was  the  blue  dolomitic  limestone  (Lower  Carboniferous),  in  which  the  Leadville  ores  occur,  taken  either  from 
open  quarries  or  from  dead- work  in  some  of  the  mines.  In  the  latter  case  it  often  carried  a  small  percentage  of  silver. 
Experiments  showed  that  dolomite  was  a  less  favorable  flux  than  pure  carbonate  of  lime,  and  since  the  advent  of 
the  railroad  limestone  has  been  obtained  from  the  beds  of  the  Colorado  Cretaceous  formation'at  Canon  City,  117 
miles  distant,  and  more  recently  still  from  a  bed  in  the  Upper  Coal  Measures  at  Robinson,  16  miles  distant  by  rail, 
where  it  costs  $3  per  ton  f.  o.  b.  Red  hematite  iron  ore  was  at  first  exclusively  used  as  a  flux,  being  principally 
obtained  from  the  Breece  iron  mine,  where  it  occurs  in  large.masses  between  the  White  and  the  Gray  porphyry,  and 
it  is  said  to  carry  a  small  percentage  of  silver.  More  recently  it  has  been  the  practice  in  many  smelters  to  use  the 
limonite  which  had  collected  on  the  dumps  of  the  various  mines,  and  which  also  carries  a  small  percentage  of  silver. 
IH  many  cases  the  ores  themselves  are  so  ferruginous  that  but  little  additional  iron  is  required. 

FUEL. — The  fuels  used  are  coke  and  charcoal.  Previous  to  the  advent  of  the  railroad  coke  was  scarce  and 
dear,  having  to  be  brought  30  to  150  miles  by  ox  or  mule  teams;  hence  charcoal  was  mu"-h  more  largely  used 
than  at  present.  This  is  furnished  by  the  forests  of  spruce  covering  the  neighboring  mountain  slopes.  The  charcoal 
produced  from  these  woods  varies  greatly  in  quality,  according  to  whether  it  has  been  burned  in  pits  or  in  kilns.  The 
pit-charcoal  made  in  the  neighborhood  of  Leadville  is  said  to  contain  2.5  per  cent,  of  ash;  a  sample  of  kiln  charcoal 
was  found  by  Mr.  Guyard  to  contain  1.62  per  cent,  of  ash.  One  hundred  and  forty-two  and  one-half  bushels  of 
charcoal  make  1  ton,  the  bushel  weighing  14  pounds. 

COKE. — The  cokes  used  are  brought  from  El  Moro,  in  the  southern  part  of  the  state,  by  the  Denver  and  Rio 
Grande  railroad,  and  from  Como,  in  the  South  Park,  by  the  Denver,  South  Park,  and  Pacific  railroad.  These 
cokes  are  made  from  coals  of  the  Lignitic  or  Upper  Cretaceous  formation,  and  contain,  according  to  determinations 
made  at  the  smelting  works  of  Messrs.  Billings  &  Eilers,  22  per  cent,  of  ash  for  the  El  Moro  and  0$  per  cent,  of 
ash  for  the  South  Park  coke.  The  composition  of  the  ash  of  the  El  Moro  coke  is  represented  as  being  84J  per  cent, 
silica,  7.1  per  cent,  peroxide  of  iron,  and  8.4  per  cent,  alumina,  lime,  etc.  The  ash  of  the  South  Park  coke  shows 
29.1  per  cent,  silica,  47.8  per  cent,  peroxide  of  iron,  and  23.1  per  cent,  alumina,  lime,  etc.  About  40  pounds  of  coke 
make  one  bushel ;  hence,  50  bushels  make  one  ton. 

ORE  BUYING. — Ore  is  purchased  either  directly  from  the  mines  themselves  for  cash  or  from  sampling  works, 
which  either  buy  from  the  mines  or  act  as  their  agents.  Various  considerations  affect  the  price  paid.  From  tbe  assay 
value  of  the  ore  in  silver  a  certain  percentage  is  deducted  for  loss  in  smelting,  which  varies  according  to  the  nature 
of  the  ore,  whether  siliceous,  ferruginous,  or  sulphnreted,  or  according  to  a  special  arrangement  made  between  the 
mine  owners  and  the  smelter  owners.  A  further  variable  charge  is  made  for  cost  of  treatment,  which  is  dependent 
on  the  nature  of  the  ore  and  its  tenor  in  lead.  As  a  general  rule,  in  regard  to  oxidized  ores,  the  charge  for  treatment 
is  lower  the  larger  the  percentage  of  lead  they  contain.  When  this  tenor  is  between  5  and  30  per  cent,  the  lead  is 
paid  for  at  from  15  to  45  cents  a  unit  of  20  pounds;  the  higher  the  percentage  of  lead  the  higher  the  price  paid  per 
unit.  When  the  ore  contains  less  than  a  certain  percentage  of  lead,  which  varies  with  the  quality  of  the  ore,  the 
mine  owner  receives  no  remuneration  for  the  lead  contained  in  his  ore.  however  rich  it  may  be  in  silver.  The 
following  table  gives  a  specimen  of  the  rates  charged  for  treatment  of  the  ores  of  some  of  the  best-known  mines, 
the  deduction  made  for  loss  of  silver,  and  the  price  paid  for  each  unit  of  lead  above  this  certain  percentage : 


Hame  of  mine. 

Deduction 
for  loss  of 
silver 
in  smelting. 

Cost  of  treat 
ment  per 
ton  of  ore. 

Price  of  lead 
per  unit  of 
20  pounds. 

Percent. 

10 

$25 

»0  25 

Chrysolite                      

5 

20 

25 

5 

22 

25 

7} 

20 

25 

7| 

28 

25 

5 

15 

30 

6 

18 

30 

6 

21 

25 

VOL  13 19 


290 


PRECIOUS  METALS. 


These  figures  vary  from  month  to  month  unless  a  time  contract  has  been  entered  into,  and  are  governed  by 
the  market  quotations  of  silver  and  lead  at  New  York  and  the  prices  of  coke,  charcoal,  and  fluxes  at  Leadville. 
Gold,  when  present  in  excess  of  one-tenth  of  an  ounce  to  the  ton,  is  paid  for  at  the  rate  of  $18  per  ounce.  The 
transportation  of  ore  from  the  mines  to  the  sampling  or  smelting  works  is  paid  for  by  the  smelters  at  the  rate  of 
$1  to  $1  85  per  ton. 

STIFLING. — When  the  ore  arrives  at  the  sampling  works,  it  is  weighed  in  the  wagon  on  scales  generally 
occupying  a  detached  building.  It  is  then  thrown  into  bins  or  piles  in  the  open  yard,  every  tenth  shovelful  as  a 
rule  being  put  into  a  wheelbarrow.  The  sample  thus  obtained  is  spread  out  on  the  sampling  floor,  and  in  the  case 
of  a  sand  ore  is  worked  up  directly  to  obtain  a  thorough  mixture.  Hard  ores  are  first  passed  through  Cornish  rolls. 
When  the  ore  is  thoroughly  mixed,  it  is  repeatedly  quartered  till  a  sample  convenient  for  drying  has  been  obtained. 
After  drying  it  is  further  crushed,  mixed,  and  quartered,  and  a  portion  is  then  ground  on  the  bucking  plate  by 
the  bncker  (a)  until  it  passes  through  a  sieve  of  70  to  80  meshes  to  the  linear  inch.  The  sample  is  then  divided 
into  three  portions,  one  of  which  is  assayed  at  the  smelter,  and  a  second  at  the  mine  or  by  a  public  assayer  who  may 
be  employed  by  the  mine.  If  the  results  of  the  two  assays  agree  closely,  a  mean  is  generally  taken  as  the  true 
value  of  the  load ;  otherwise  the  third  portion  is  sent  for  control  to  a  third  independent  assayer.  Sand  ores  require 
no  crushing  before  charging  into  the  furnace.  For  hard  ores,  slags,  fluxes,  etc.,  Blake,  and  occasionally  Alden 
crushers,  driven  by  steam-power,  are  employed. 

SMELTING  CHARGES. — The  construction  of  ore-beds  is  carried  on  to  a  considerable  extent  at  both  smelting  and 
sampling  works.  These  beds  average  from  100  to  180  tons  each  in  weight,  and  contain  approximately  equal  parts 
(20  to  25  per  cent.)  of  metallic  lead,  metallic  iron,  and  silica,  of  which  the  proportion  of  lead  is  subject  to  the 
greatest  fluctuation.  The  proportion  of  silver  to  lead  is  1  ounce  to  about  6  or  8  pounds.  Stilphureted  ores  are 
not  roasted,  but  are  thrown  directly  into  the  furnace,  and  are  mixed  in  small  quantities  with  the  oxidized  ores. 

The  charges  vary  so  greatly  in  composition  at  the  different  smelters  that  it  is  hardly  possible  to  give  that  of 
an  average  one.  At  first  the  aim  seems  to  have  been  to  produce  a  normal  singulo  silicate  slag,  but  a  change  has 
been  gradually  taking  place  to  slags  of  a  slightly  more  acid  character,  containing  from  32  to  36  per  cent,  of  silica. 
At  one  smelter  the  aim  is  said  to  have  been  to  produce  a  slag  in  which  the  proportion  of  earthy  base  to  metallic 
base  should  be  as  one  to  two,  or  to  some  even  number.  The  following  examples  of  different  charges  are  taken  from 
Mr.  Guyard's  report  as  specimens  of  their  variable  character : 


I. 

II. 

HI. 

rv. 

1 

V. 

On: 

Pound*. 

Pound*. 

Pound*. 

Pound*. 

Pound*. 

100 

200 

123 

500 

50 

300 

183 

200 

645 

10 

306 

700 

ft,*  It 

FLUX: 

10 

to 

90 

80 

62 

10 

7 

170 

Sla" 

30 

150 

60 

80 

80 

167 

330 

FUEL: 

15 

80 

50 

95 

80 

Coke                   

20 

60 

50 

65 

60 

100 

160 

110 

Total  weight  of  charge  

235 

850 

563 

1,  1UO 

9ii7 

The  proportions  of  charcoal  and  coke  in  the  fuel  vary,  according  to  supply  and  cost  and  from  other 
considerations,  within  the  limits  of  three  parts  of  the  one  to  four  of  the  other. 

The  table  on  page  291  gives  the  calculations  made  by  Mr.  Guyard  from  data  obtained  for  the  census  year  in  eight 
of  the  principal  smelting  works  of  Leadville:  First,  the  average  proportion  of  flux  to  100  parts  of  ore;  second,  the 
proportion  of  fuel  to  100  parts  of  ore ;  third,  the  proportion  of  fuel  to  100  parts  of  smelting  charge.  In  the  fourth 
rubric  is  given  the  number  of  tons  smelted  per  twenty-four  hours  in  each  of  these  works.  From  these  data  he 
calculates  the  relation  of  actual  to  nominal  smelting  capacity  as  varying  from  20  to  80  per  cent.  Furnace  III  is 
regarded  as  fulfilling  most  nearly  theoretically  perfect  conditions. 

a  The  bucking  plate  in  ordinary  use  in  assay  offices  in  the  West  is  a  cast-iron  plate  measuring  2  by  H  feet,  with  flanges  on  the  long 
side  rising  half  an  inch  above  the  surface ;  the  latter  is  planed  down,  but  uot  polished.  The  buckcr  or  rubber  is  a  rectangular  piece  of  cast 
iron  7  by  5  inches,  and  from  1  to  4£  inches  thick.  On  the  upper  surface  is  a  socket  for  a  long  wooden  handle,  and  the  lower  surface  is 
curved  (a  portion  of  a  large  cylindrical  snrfacc)  so  that,  as  the  operator  pushes  it  to  and  fro  on  tho  plate  to  pulverize  the  ore,  a  slight 
rocking  motion  may  be  given  at  the  same  time,  which  brings  the  particles  under  the  bncker  instead  of  pushing  them  before  it. 


LEAD  SMELTING  AT  LEADVILLE,  COLORADO. 


291 


« 

I. 

11. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

Proportion  of  flux  to  100  parts  ore 

25  00 

39  Q 

4°  0 

24  0 

28.  8 

33C 

Proportion  of  furl  to  100  parts  ore  

45  33 

33  0 

33  8 

18  5 

25  o 

!'•    ° 

"5  0 

Proportion  of  fuel  to  100  pnrts  chargm  

3G  00 

23  5 

23  7 

15  0 

19  3 

31  5 

18  5 

18.  60 

Tons  of  ore  smelted  per  twent  y-fonr  hours  

28.00 

104.0 

51.0 

11.  5 

23.0 

15.9 

69.5 

32.60 

The  proportions  obtained  by  Mr.  Guyard  as  an  average  for  the  entire  camp  during  the  census  year  are: 

32.83  parts  fuel  to  100  parts  ore. 
23.G5  parts  fuel  to  100  parts  charges. 

Tie  calculates  that  88  per  cent,  of  the  lead  iu  the  ore  is  extracted  as  bullion  by  direct  smelting,  the  remainder 
going  into  the  slag  and  escaping  up  the  stack;  also  that  1£  parts  of  fuel  are  required  for  each  unit  by  weight  of 
bullion  produced. 

In  the  following  table  Mr.  Guyard  has  calculated  with  regard  to  the  same  furnaces  shown  in  the  preceding 
table:  First,  percentage  of  lead  extracted  in  smelting  in  the  form  of  bullion;  second,  the  percentage  of  silver 
extracted;  third,  the  average  charges  for  smelting  per  ton  of  ore  at  each  establishment;  fourth,  the  cost  to  the 
smelter  of  treating  each  ton  of  ore;  fifth,  the  average  assay  of  slags  in  ounces  of  silver  per  ton;  sixth,  the  average 
assay  of  flue-dust  in  ounces  of  silver  per  ton : 


I. 

II. 

m. 

IV. 

V. 

VI. 

VII. 

VIII. 

Percentage  of  lead  extracted  in  smelting  

85  to  88 

86  to  91 

88.0 

85  to  95 

85  to  90 

90  to  93 

87  0 

90  0 

Percentage  of  silver  extracted  in  smelting  . 

100 

95  to  97 

97  0 

88  to  95 

95  0 

97  0 

98  5 

97  5 

Charges  for  smelting  per  ton  of  ore  

$15  to  $30 

$15  to  $30 

$15  to  $30 

*i<>  to  *°5 

$16  to  $30 

$15  to  $30 

$15  to  $30 

$15  to  $30 

Cost  for  smelting  per  ton  of  ore  

$12  to  $18 

$18  to  $23 

$10  to  $15 

$13  to  $16 

$15  to  $18 

$13 

$13  68 

415 

Average  assay  of  slaps  in  ounces  of  silver  

2 

4 

0  5 

1  5 

1  5 

1  5 

1.5 

4  0 

Average  ansav  of  fluo-dnsl  in  ounces  of  silver  

36 

37 

36.0 

35  0 

35  0 

36.0 

36.0 

37  0 

The  above  table  shows  only  the  conditions  Which  obtained  during  the  year  ending  June  1,  1880.  These  have 
been  varied  since  that  time  by  a  general  reduction  of  the  smelting  charges,  owing  to  competition  and  to  the 
cheapening  of  supplies,  and  also  by  the  reduced  tenor  of  the  ore  in  silver.  The  proportion  of  sulphureted  over 
oxidized  ores  will  also  probably  increase  as  time  goes  on. 


GENERAL  SMELTING  OPERATIONS. 

BLOWING-IN  OF  FURNACES. — The  furnace  is  first  dried  by  means  of  a  slow  charcoal  or  wood  fire,  whose 
temperature  increases  gradually  for  several  days.  When  the  drying  is  completed,  the  fire  is  allowed  to  burn  out 
and  the  furnace  left  to  cool.  The  crucible  is  then  lined  with  steep  or  brasque;  tamping,  a  simple  lining  of  fire-clay, 
is  sometimes  put  upon  the  dam,  siphon,  and  siphon-tap.  The  furnace  is  then  filled  to  the  feed-hole  with  charcoal, 
the  tuyere-holes,  tyinpstone,  and  stack-damper  being  left  open  to  create  »  draught.  The  charcoal  gradually 
becomes  incandescent  to  the  very  throat.  When  this  zone  has  reached  a  low  red  heat  the  blowing-ill  begins.  The 
tuyere  holes  of  the  water-jacket,  with  the  exception  of  from  two  to  four  of  those  nearest  the  front,  are  sealed  with 
plugs  of  clay,  and  the  wind-bags  of  the  corresponding  tuyeres  are  tied  up  with  strings.  Tuyeres  are  inserted  in  the 
holes  left  open;  the  tyinpstone  is  set  in,  and  the  blast  then  turned  on  at  full  pressure.  A  long  flame  issues  from 
the  siphon-tap,  and  the  fire  is  kept  steadily  up  until  the  lead-well  becomes  red  hot.  The  remaining  tuyere-holes  art- 
then  opened  and  all  the  tuyeres  are  set  in.  The  blast  is  regulated  to  the  normal  pressure,  and  the  furnace  is  now 
ready  for  the  filling  of  the  crucible. 

FILLING  OF  THE  CRUCIBLE. — Bars  of  bullion  kept  in  reserve  for  this  purpose,  in  amount  varying  from  4  to 
12  tons,  according  to  capacity,  are  thrown  in  at  the  feed-door  with  more  fuel,  the  proportion  being  three  bars  of 
bullion  (300  pounds)  to  eight  shovels  of  charcoal,  or  about  14  per  cent,  of  fuel.  From  100  to  150  bushels  of  charcoal, 
according  to  the  capacity  of  the  furnace,  are  consumed  during  the  blowing-in.  When  molten  lead  makes  its 
appearance  in  the  lead-well,  a  few  pieces  of  live  charcoal  are  placed  on  it  to  prevent  it  from  cooling,  and  the 
furnace  is  ready  for  charging. 

CHARGING  OP  THE  FURNACE.— Old  slags  are  first  of  all  thrown  into  the  furnace  as  a  test  of  its  temperature, 
which  is  not  ready  until  the  slag  is  perfectly  fluid.  The  head  smelter  or  his  assistant  opens  the  tap-hole  in  the 
tyinpstone  from  time  to  time  to  observe  their  degree  of  fluidity,  and  the  regular  charging  begins  only  when  they  run 
quite  freely.  The  charges  are  disposed  on  the  inside  of  the  furnace  next  to  the  walls,  a  depression  being  left  in  the 
center  for  the  fuel.  This  is  the  mode  of  charging  generally  adopted,  but  there  are  variations  in  the  manner  of 
mixing  the  materials  forming  the  smelting  charges.  At  some  of  the  smelting  works  fuel  is  first  thrown  in,  then  old 
slags,  above  these  the  fluxes,  and  then  the  ore;  at  others  fuel  is  mixed  with  the  old  slags  and  fluxes  with  the  ores. 
The  mode  of  proceeding  generally  adopted,  however,  is  to  mix  slags,  fluxes,  and  ore  together  and  keep  the  fuel 


292  PRECIOUS  METALS. 

separate.  At  the  most  successful  establishment  the  method  of  mixing  fuels  and  old  slags  on  the  one  hand  and 
fluxes  and  ore  on  the  other  prevails.  In  either  case  the  distribution  of  the  materials  in  the  furnace  is  the  same;  i.  e.t 
fael  is  thrown  in  the  center  and  the  charge  is  distributed  around  it. 

TAPPING  OP  SLAGS. — The  tapping  of  slag  commences  as  soon  as  the  furnace  is  in  regular  operation,  and 
occurs  generally  every  fifteen  or  twenty  minutes,  although  a  few  works  have  adopted  the  method  of  continuous  flow 
from  the  tap-hole.  The  tap-hole  is  closed  by  a  lump  of  clay  at  the  end  of  an  iron  tupping-rod.  The  slag  is  caught 
directly  in  a  slag-buggy  or  conical  cast  iron  pot  mounted  ou  wheels,  and  is  either  allowed  to  solidify  entirely  in 
the  pot  and  then  thrown  out  and  broken  up,  or  it  is  wheeled  to  the  edge  of  the  slag  heap  and  tipped  over  so  that  it 
runs  in  a  half  liquid  state  down  the  sides  of  the  dump.  A  single  smelter  adopts  the  plan  of  allowing  the  slag  to 
solidify  partially  in  the  pot,  and  of  then  making  holes  through  the  hardened  crust  and  tipping  the  pot  over  so  that 
the  still  molten  material  runs  out,  leaving  a  shell  over  2  inches  thick.  This  shell  is  easily  broken  up  for  re-smelting, 
it  having  been  found  that  it  is  a  little  richer  in  silver  than  the  center.  Slag  samples  for  assay  are  taken  two  or 
three  times  a  day  from  the  stream  in  the  slag  gutter,  and  their  specific  gravity  and  contents  in  lead  and  silver  are 
determined  in  the  assay  office.  Any  speiss  or  matte  that  may  be  formed  is  run  into  the  slag-pot  with  the  slag,  and 
iseither  thrown  out*vith  the  latter  upon  the  dump,  or,  after  cooling,  is  detached  from  the  slagand  preserved  separately. 
The  proportion  of  speiss  and  matte  at  Leadville  is  generally  very  small. 

LADLING  OP  BULLION. — As  often  as  necessary  the  bullion  is  dipped  out  of  the  lead-wells  with  wrought-iron 
ladles  and  poured  into  cast-iron  molds.  At  a  single  smelter  a  different  method  obtains.  The  bullion  is  tapped 
periodically  from  an  opening  in  the  clay  lining  of  the  lead- well  into  an  iron  pot  mounted  ou  a  small  stove,  in  which 
a  light  fire  is  kept  burning.  From  this  pot  it  is  ladled  into  the  molds.  The  advantages  of  this  method  are  that 
the  surface  of  the  lead  in  the  well  is  kept  covered.  The  lead  is  therefore  hotter,  and  the  passage  into  the  crucible  is 
more  readily  cleaned.  Moreover,  the  lead  being  drawn  from  below,  the  surface  is  free  from  skimmings,  and  the 
bars  are  smoother  and  cleaner. 

The  bars  of  bullion  are  then  sampled,  weighed,  and  marked.  The  sampling  is  done  by  taking  with  a  scoop- 
chisel  a  piece  from  the  top  and  a  piece  from  the  bottom  of  each  bar.  The  samples  from  200  bars,  or  10  tons,  which 
constitute  a  car-load,  are  sent  to  the  assay  office,  where  they  are  melted  together  and  cast  into  a  small  bar,  from 
which  pieces  are  taken  for  an  assay. 

CONTROL  OF  SMELTING  OPERATIONS. — From  time  to  time  the  siphon-tap  has  to  be  cleared  by  the  insertion 
of  a  curved  iron  rod,  about  2  inches  thick,  previously  heated  to  redness  at  the  curved  end. 

The  tuyeres  must  be  watched  from  the  sliding  valve,  and  when  dark  rings  of  chilled  slag  are  observed  around 
them  they  are  removed  by  iron  rods  inserted  through  the  tuyere,  and  the  temperature  is  raised  by  the  addition  of 
more  fuel  or  by  a  reduction  in  the  proportion  of  charge. 

The  water-jackets  require  constant  watching,  in  order  that  the  temperature  of  the  water  issuing  from  them 
may  be  kept  as  nearly  as  possible  at  from  50°  to  60°  C. 

The  blast  also  requires  constant  attention  and  regulating,  the  pressure  being  increased  or  diminished  as  the 
condition  of  the  furnace,  determined  by  observation  from  the  tuyeres,  may  demand. 

If  semi-fluid  slags  or  raw  ore  form  accretions,  which  do  not  disappear  by  an  increase  of  the  temperature,  the 
blast  must  be  shut  off,  the  tympstone  removed,  and  the  hearth  cleaned  by  means  of  bars  and  sledges;  after  which 
a  little  fuel  is  thrown  into  the  hearth,  the  tympstoue  is  replaced,  and  the  blast  is  turned  on  again.  At  one  period  ores 
rich  in  lead  were  scarce  at  Leadville,  and  the  charges  generally  contained  much  less  than  the  normal  20  to  25  per 
cent,  of  lead.  The  running  of  the  furnace  became,  in  consequence,  a  much  more  difficult  matter,  and  the  formation 
of  obstructions  of  various  kinds  was  of  frequent  occurrence. 

When  accretions  form  on  the  walls  of  the  shaft,  it  is  necessary  to  "bar  it  out"  once  in  twenty -four  hours,  or 
once  per  shift,  as  the  case  may  be.  To  accomplish  this  charging  is  interrupted  until  the  contents  of  the  furnace 
descend  to  the  level  of  the  accretion.  The  blast  is  then  turned  off,  a  long  chisel  pointed  bar  is  introduced  into  the 
feeding  hole  of  the  furnace,  and,  being  inserted  between  the  accretion  and  the  furnace  wall,  is  struck  with  sledge- 
hammers until  the  accretion  is  detached,  when  the  blast  is  turned  on  again  and  the  charging  resumed. 

The  Leadville  furnaces  are  generally  run  with  a  dark  top;  i.  e.,  the  zone  at  the  throat  is  so  dark  that  no  flames 
issue  from  it,  and  only  a  black  smoke  is  seen  ascending  the  chimney.  This  appearance  is  an  indication  that  the 
furnace  is  running  properly. 

SMELTING  OF  FLUE-  AND  CHAMBER-DUST. — Flue-  and  chamber-dust  are  mixed  in  general  with  lime,  and  the 
mixture  may  or  may  not  be  molded  into  bricks.  It  is  then  spread  over  the  ore  beds,  so  that  a  little  of  the  flue-dust 
enters  into  the  composition  of  the  smelting  charges. 

BLOWING-OUT  OF  FURNACE.—  This  takes  place  when  the  furnace  needs  repairing,  or  when  an  accident, 
interfering  with  the  regular  working  of  the  furnace,  has  occurred.  It  is  done  by  suspending  the  charges  and 
continuing  the  blast  until  the  whole  contents  of  the  furnace  are  molten.  The  charge  soon  burns  with  a  bright  top, 
and  the  furnace  emits  torrents  of  heavy  white  fumes.  When  the  whole  charge  has  reached  the  level  of  the 
tuyeres  the  furnace  is  emptied  of  its  fluid  contents,  first  from  the  tap-hole,  then  the  breast  is  removed,  and  the 
bullion  is  taken  out  of  the  crucible. 

LENGTH  OF  RUN. — The  smelting  campaigns  are  seldom  less  than  three  weeks,  and  often  reach  six,  eight,  and 
even  thirteen  months. 


LEAD  SMELTING  AT  LEADVILLE,  COLORADO. 


293 


FURNACE  PRODUCTS. 

BULLION.— The  bullion  of  Leadville  is  generally  very  pure,  its  constituents  other  than  lead  and  silver,  though 
numerous,  being  present  in  very  small  quantity.  The  character  of  these  impurities  is  shown  in  the  following 
analyses  made  by  Mr.  Guyard,  I  being  bullion  from  the  La  Plata  smelter,  II  being  a  mixture  of  equal  parts  of 
bullion  from  nine  different  smelters : 


I. 

n. 

Lead  (by  difference)  

99  0798210 

98  492379 

Silver  

0  6112445 

Gold  

0  0000888 

Copper  

0  0479100 

Tin  

Bisnmth  

Arsenic  

0  0391365 

Antimony  

0  °138940 

Iron  

0  0063000 

0  012600 

Zinc  

0  0016052 

0  00023° 

Cadmium  » 

Sulphur  

100 

100 

Onncefl  of  silver  to  the  ton 

178.275 

231  408 

Ounces  of  gold  to  the  ton 

0  026 

0  260 

The  presence  of  tin  in  the  bullion  seems  rather  singular,  inasmuch  as  it  has  not  been  detected  in  any  of  the 
ores  or  fluxes  of  Leadville.  It  has  been  suggested  that  it  owed  its  origin  to  the  great  number  of  preserved-frnit  cans 
scattered  about  the  place,  some  of  which  may  have  found  their  way  into  the  furnace.  It  is  indeed  said  that  these 
cans  were  at  one  time  used  at  one  smelter,  probably  as  a  precipitant  for  the  lead  in  the  galena.  As  tin  has  also 
been  found  in  other  products  at  different  times,  it  seems  hardly  probable  that  this  source  can  be  adopted  as  that 
from  which  it  is  in  all  cases  derived. 

The  average  assay  of  bullion  shipped  from  Leadville  during  the  early  part  of  the  census  year  was  nearly  300 
ounces  to  the  ton,  but  during  the  month  of  December,  1880,  it  had  fallen  off  to  less  than  200  ounces.  Mr.  Guyard 
estimates  the  average  loss  of  silver  in  smelting  at  4.115  per  cent.,  and  of  lead  at  ll.GS  per  cent.,  part  of  which, 
however,  is  recovered  from  the  chamber-  and  flue-dust  The  bars  of  bullion  weigh  on  an  average  100  pounds  each, 
200  bars,  or  10  tons,  constituting  a  car-load.  They  are  shipped  to  eastern  refineries,  and  when  sold  direct  the  latter 
pay  the  cost  of  transportation,  which  varies  from  $27  to  $35  per  ton.  The  price  of  lead  in  bullion  is  subject  to  great 
fluctuation,  and  has  varied  between  $30  and  $78  per  ton  at  Leadville,  the  average  price  being  $60.  Payments  are 
made  for  bullion  at  New  York  quotations,  deducting  for  the  cost  of  refining  3  ceuts  per  ounce  of  silver,  or  sometimes 
$14  to  $15  per  ton  of  bullion.  In  other  cases  the  charges  are  3  ounces  of  silver  and  5  per  cent,  of  lead  per  ton. 

SLAG. — The  slags  produced  at  Leadville  are  in  some  instances  normal  singulo-silicates,  but  in  general  rather 
more  acid,  the  object  in  producing  the  latter  being  to  insure  a  smoother  run  of  the  furnace,  to  require  less  constant 
watching  and  to  avoid  the  formation  of  sows  and  accretions.  They  flow  freely,  and  generally  possess,  when  cold,  a 
compact,  fine-grained  structure,  though  frequently  well  crystallized  in  parts.  They  are  for  the  most  part  strongly 
magnetic ;  aud  Mr.  Guyard  has  shown  that  this  property  is  not  due  to  any  magnetic  silicate  of  iron,  but  to  magnetic 
oxide  of  iron,  he  having  isolated  these  substances  in  a  greater  or  less  quantity  aud  in  a  state  of  perfect  purity  from 
all  slags  investigated  by  him.  As  a  means  of  judging  whether  the  slag  is  normal  in  its  composition  and  contains 
any  excess  of  lead  determinations  are  made  daily  at  a  few  of  the  smelters  by  means  of  the  Jolly  spi  ing- balance. 
Slags  from  a  normal  run  carry  from  2  to  4  per  cent,  of  lead  and  from  2  to  4  ounces  of  silver  to  the  ton,  though  by 
attention  and  careful  charging  these  figures  are  sometimes  greatly  lowered.  On  the  other  hand,  they  frequently 
rim  much  higher,  both  in  lead  and  in  silver,  owing  to  the  faulty  composition  of  the  charges  or  to  careless  regulation 
of  the  smelting  process.  Slags  from  the  earlier  campaigns  of  some  furnaces  have  been  found  to  coutaiu  as  much 
as  15  to  20  per  cent,  of  lead,  and  silver  in  proportion ;  in  view  of  which  it  is  hardly  a  matter  of  wonder  that  failures 
were  frequent.  Slags  accidentally  rich  in  silver,  and  whole  slag  heaps  from  some  of  the  works  first  started  are 
re-smelted  with  the  ores. 

MATTES. — Since  the  sulphide  ores  occurring  in  the  region  are  not  roasted,  but  thrown  directly  into  the 
furnace,  mixed  iu  small  proportion  with  the  oxidized  ores,  a  certain  amount  of  matte  is  necessarily  formed,  which 
consists  mainly  of  sulphides  of  iron  and  lead,  with,  as  ascertained  by  Mr.  Guyard,  a  large  percentage  of  magnetic 
oxide  of  iron.  These  mattes  carry  from  40  to  90  ounces  of  silver  to  the  ton,  and  are  roasted  iu  heaps  preparatory 
to  being  re  smelted. 


294  PRECIOUS  METALS. 

SPEISS. — Speiss,  which  is  fouud  only  in  small  quantity,  is  an  iron  sulph-arsenide,  and  seems  to  concentrate  in 
itself  all  the  molybdenum  as  well  as  most  of  the  nickel,  traces  of  which  exist  in  the  ores.  It  is  further  characterized 
by  its  very  small  percentage  of  antimony,  and,  according  to  Mr.  Guyard,  by  the  total  absence  of  cobalt.  It  is  a 
question,  however,  whether  an  examination  of  a  large  number  of  samples  would  justify  the  conclusion  drawn  by 
Mr.  Guyard  that  a  complete  separation  of  nickel  and  cobalt  is  effected  in  the  smelting  process.  Ho  fouud  cobalt 
without  nickel  in  the  skimmings  from  the  lead-wells  and  nickel  without  cobalt  in  the  speiss. 

Its  silver  contents  vary  from  2  to  4  ounces  per  ton.     It  is  not  roasted  or  subjected  to  any  further  treatment. 

ACCIDKNTAL  FORMATIONS  IN  THE  FURNACE.— Among  these  iron  sows  are  the  most  important,  and  have 
frequently  been  the  source  of  much  trouble,  sometimes  necessitating,  as  before  mentioned,  the  blowing-out  of  a 
furnace  in  order  to  effect  their  removal.  Besides  ordinary  hearth  obstructions,  different  shaft  accretions  are  found 
in  varying  quantity,  which  it  is  unnecessary  here  to  discuss  further,  save  to  quote  an  instance,  mentioned  by  Mr. 
Guyard,  of  a  small,  round  furnace  entirely  lined  from  the  water  jackets  to  within  6  inches  of  the  feed-hole  with  one 
of  these  accretions  a  foot  in  thickness. 

FLUE-  AND  CHAMBER  DUST. — Leadville  being  situated  at  an  elevation  of  10,000  feet  above  the  sea,  the  volume 
of  air  blown  into  S  furnace  with  a  given  blast-pressure  is  far  greater  than  with  the  same  pressure  at  sea-level; 
consequently  the  draught  of  the  furnace  is  correspondingly  increased,  and  the  quantity  of  dust  and  fumes  escaping  by 
the  stack  is  very  large.  This  would  seem  to  necessitate  the  employment  of  a  very  perfect  system  of  condensing  tines 
and  chambers.  In  point  of  fact,  however,  as  has  been  seen,  these  arrangements  are,  with  one  or  two  exceptions, 
very  poor;  consequently  a  large  proportion  of  the  dust  and  fumes  is  lost  in  the  air.  Their  composition  is  extremely 
complicated,  and  is  characterized  by  the  presence,  in  considerable  quantities,  of  chlorides,  bromides,  iodides,  and 
phosphates.  They  carry  from  1^5  to  60  per  cent,  of  lead,  the  latter  figure  applying  to  the  fumes  condensed  in  the 
Bartlett  filter  before  described,  and  from  30  to  40  ounces  of  silver  to  the  ton,  although  the  Bartlett  filter  fumes 
held  but  4.3  ounces.  The  composition  of  the  latter  is  otherwise  remarkable  in  that  they  contain  over  11  per 
cent,  of  phosphate  of  lead,  9  per  cent,  of  chloro-bromo-iodide  of  lead,  and  18  per  cent,  of  sulphide  of  lead,  and 
from  the  further  fact,  according  to  Mr.  Guyard,  that  iron,  zinc,  and  manganese  exist  in  them  entirely  in  the  state 
of  sulphides.  It  must  be  borne  in  mind,  however,  that  these  fumes  were  condensed  at  a  distance  of  200  feet  from 
the  furnace.  Mr.  Guyard  has  calculated  the  weight  of  calcined  dust  collected  from  one  furnace  of  30  to  40  tons 
capacity  during  twenty-four  hours  at  1,400  pounds,  and  estimates  that,  where  the  niter  is  not  employed,  the  loss  of 
lead  equals  half  a  ton  and  of  silver  4£  ounces  per  day  per  furnace.  On  this  assumption  more  lead  is  lost  in  the  air 
than  is  collected  in  the  dust-chambers.  As  already  shown,  the  chamber-  and  flue-dust  is  mixed  with  lime  and  thrown 
over  the  ore-beds  to  be  re-smelted.  In  one  case,  however,  a  furnace  was  specially  constructed  for  the  purpose  of 
roasting  the  due-dust,  though  with  what  object  in  view  it  is  impossible  to  say,  unless  on  the  erroneous  supposition 
that  much  arsenic  is  present.  In  point  of  fact,  arsenic  is  found  in  it  in  only  small  quantities,  and  this  roasting 
deprives  the  dust  of  the  carbon  which  would  otherwise  suffice  for  the  reduction  of  all  the  lead  contained  in  it, 
besides  occasioning  the  loss  of  some  silver.  In  another  smelter  the  flue-dust  is  prepared  for  re-smelting  by  melting 
down  in  a  reverberatory  furnace,  at  first  with,  and  now  without,  the  addition  of  slag.  It  is  then  run  out,  and 
after  cooling  it  is  broken  up  and  mixed  with  the  charges. 

COST  OF  LABOR  AND  MATERIAL. 

Below  are  given  a  few  data  relative  to  the  prices  paid  for  fluxes,  fuel,  and  the  average  wages  of  employes 
during  the  census  year  at  Leadville,  which  serve  to  give  a  fair  idea  of  the  economic  conditions  of  smelting  at  that 
time: 

Dolomite,  per  ton $3  00  to  $4  00 

Hematite,  per  ton 8  00  to  11  50 

Charcoal,  per  bushel 10  to        18 

Coke,perton v 25  00  to  60  00 

Piue  wood,  per  cord  of  2,000  to  3,000  pounds 4  50  to    5  00 

Foremen,  per  shift  of  eight  to  twelve  hours 3  00  to    6  00 

Head  smelters,  per  shift  of  eight  to  twelve  hours 3  00  to    4  25 

Slag  wheelers,  per  shift  of  eight  to  twelve  hours 2  50  to    4  00 

Feeders,  per  shift  of  eight  to  twelve  hours 3  00  to    4  00 

Helpers,  per  shift  of  twelve  hours 2  50  to    3  00 

Day  laborers,  per  s'lift  of  ten  to  twelve  hours , 2  50 

Engineers,  per  shift  of  eight  to  twelve  hours 3  50 

Fuelmen,  per  shift  of  eight  to  twelve  hours 3  00 


LEAD  SMELTING  AT  LEADVILLE,  COLORADO.  295 

CONCLUSION. — In  conclusion,  it  may  be  said  that  lead  smelting,  as  carried  on  in  tliis  region,  wliile  not  entirely 
beyond  criticism,  has  been  brought  to  a  relatively  high  degree  of  perfection,  and  is  extremely  creditable  to  American 
metallurgists.  One  of  the  most  useful  practical  lessons  that  has  been  taught  by  t  lie  comparative  success  of  I  In- 
various  smelting  works  is  that  this  has  been  proportional  to  the  more  thorough  training  in  scientific  metallurgy  of 
its  managers,  the  completeness  and  accuracy  with  which  they  have  gauged  the  operations  of  their  furnaces  by 
chemical  tests,  and  the  intelligence  witli  which  the  results  of  these  tests  have  been  applied  to  the  practical  conduct 
of  their  business. 

Could  this  lesson  overcome  the  idea  so  common  among  us  that  the  adaptability  and  "  cuteness"  of  the  American, 
which  is  in  so  many  points  acknowledged  to  be  superior  to  that  of  other  races,  enable  him  to  master  the  science 
of  smelting  as  readily  as  he  does  any  branch  of  trade,  it  might  prevent  an  increase  of  the  already  very  considerable 
number  of  abandoned  smelters  which  dot  our  western  hills  and  valleys,  and  save  a  portion  of  the  capital  which  is 
annually  wasted  through  gross  ignorance  in  the  various  operations  connected  with  mining. 


